Technical field

The present invention relates to an anionic froth flotation collector for froth flotation. Further, the invention relates to a method for producing the froth flotation collector, and a use of the froth flotation collector in froth flotation for separation of minerals, such as sulphide minerals.

Background

Flotation is one of the most important and versatile enrichment processes in the mining industry. It is a process in which selective separation of especially complex sulphide ores can be achieved.

The ore to be treated in froth flotation is in general reduced to fine particles by crushing and grinding, collectively known as comminution, so that the various minerals to as high extent as possible exist as physically separate grains. This process is known as liberation and is performed prior to the froth flotation process

Flotation is done by adding a suspension including small particles of the ore material and water to a container. Reagents are added to the container to, among other things, selectively increase the hydrophobic properties of the mineral or minerals to be separated. Air is supplied to the container while the content is agitated by mechanical or hydrodynamic means to keep the mineral afloat. The mineral that has now been made hydrophobic and becomes connected to the air bubbles, floats to the surface of the container where the air bubbles form a froth, rich in the hydrophobic minerals. The froth is then removed from the container.

The reagents used in the flotation process are typically collectors, frothers, and various regulators (activators, depressants, pH-regulators, etc). Collectors are used for modifying the hydrophobicity of the minerals by adsorption onto the mineral surface. There are different types of anionic froth flotation collectors conventionally used, whereby xanthates are the most common for sulphide ores. Regulators are used to modify the collectors' effect on the minerals and provide more selectivity regarding which material should become hydrophobic. Frothers are used to increase the stability of the froth and to prevent the air bubbles from breaking.

Typically, collectors are short alkyl chains (2-6 carbon atoms) terminated by a xanthate or thiocarbonate or other functional groups that will chemisorb or selectively physically adsorb onto the target particle surface. By lowering the surface energy, the collector facilitates particle adhesion to the air bubbles during flotation. Collectors are consumed, depending on ore properties in the amount of approx. 30-500 g per ton (1000kg) of ore, with an annual consumption growth rate of 2-3%, as a result of the annually processed quantities of ores (billions of tons) that must continuously increase to meet the growing demand for minerals and metals. Xanthates are the most used mineral collectors for sulphide ores, due to their high mineral selectivity and cost effectiveness. Sodium ethyl xanthate is classified as a 'Priority Existing Chemical' in Australia (NICNAS 2000), meaning that its manufacture, handling, storage, use or disposal may result in adverse health or environment effects. Xanthates alongside other petrochemical products cause CO2 emissions during production, use and disposal.

Using xanthates for the flotation of sphalerite (ZnS) requires the addition of copper sulphate. If copper sulphate is not added, the result is a less efficient flotation separation.

SU1191113 discloses a collector for use in flotation of iron ores. The collector consists of a combination of tall oil lignin with still bottoms. Tall oil lignin may be oil and lignin or tall oil contaminated by lignin. Still bottom comprises at least synthetic fatty acids. The iron ore must be pre-treated prior to the addition of the collector. Pre-treatment is done with NaOH, nitrolignin and carboxymethylcellulose.

US2015/0076038 discloses a froth flotation process for beneficiation and ore concentration of silicate containing minerals and ores. The cationic collectors used contain alkylether amines and alkylether diamines.

Summary

It is an aim of the present invention to at least partly overcome the above-mentioned problems, and to provide an improved froth flotation collector for use in froth flotation. The object of the disclosure is to provide a more environmentally friendly and biodegradable froth flotation collector with low carbon footprint during production, use and disposal.

This aim is achieved by a froth flotation collector for use in froth flotation for separation of minerals, such as sulphide minerals as defined in claim 1.

The froth flotation collector comprises particles of lignin at a size of 5 pm or less.

One aspect of the invention relates a froth flotation collector for use in froth flotation for separation of minerals, such as sulphide minerals, comprising or consisting of at least 20 wt% lignin particles, which particles have a size of 5 pm or less, optionally between 10 and 80 wt% of another froth flotation collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and optionally up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, b) frother, c) depressant, and d) pH regulator, wherein wt% are percentages of a total weight of the froth flotation collector.

One aspect of the invention relates to use of a froth flotation collector in froth flotation for separation of minerals, such as sulphide minerals, wherein the froth flotation collector comprises or consists of at least 20 wt% lignin particles, which particles have a size of 5 pm or less, optionally between 10 and 80 wt% of another froth flotation collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and optionally up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, b) frother, c) depressant, and d) pH regulator, wherein wt% are percentages of a total weight of the froth flotation collector.

In another aspect, the ores are grinded prior to use without any further pre-treatment or without any further chemical pretreatment. In a further aspect, the froth flotation collector is an anionic froth flotation collector. In an aspect, the froth flotation collector comprises at least one or more frothers and one or more pH regulators and at least 20 wt% lignin particles, which particles have a size of 5 pm or less.

Lignin is an organic material found as a natural element in plants and trees. Lignin is one of the most abundant natural organic molecules on earth, exceeded only by cellulose. As an organic material, which can be found abundantly in nature, its use has little to no negative impact on the environment and is biodegradable. Also, when using lignin, waste material from the forest industry can be used. Surprisingly, it has been found that using lignin particles smaller than 5 pm as a collector results in an efficient flotation. Tests have shown that using lining particles smaller than 5 pm as a collector results in a more efficient flotation than using lignin particles of larger sizes. The reason for this may be that particles of lignin at a size of 5 pm or less, allows the collector to be better distributed in the suspension and increases the probability for mineral-collector collision and adhesion, than using lignin of larger sizes.

According to some aspects, at least 50 wt-% of the particles of lignin have a size of 1 pm or less, wherein wt% are percentages of a total weight of the froth flotation collector.

According to some aspects, at least 50 wt-% of the particles are nanoparticles having a size of 600 nm or less, wherein wt% are percentages of a total weight of the froth flotation collector.

According to some aspects, at least 50 wt-% of the particles have a size of 400 nm or less, wherein wt% are percentages of a total weight of the froth flotation collector.

Tests have shown that using lignin nanoparticles as a froth flotation collector results in even more efficient flotation. Thus, smaller particle sizes result in more efficient flotation.

According to some aspects, the froth flotation collector comprises at least 50 wt % to 100 wt% of said particles of lignin, wherein wt% are percentages of a total weight of the collector.

According to some aspects, at least 20 wt-% of the froth flotation collector consists of said particles of lignin, wherein wt% are percentages of a total weight of the collector. According to some aspects, at least 40 wt-% of the froth flotation collector consist of said particles of lignin, wherein wt% are percentages of a total weight of the collector.

According to some aspects, at least 60 wt-% of the froth flotation collector consists of said particles of lignin, wherein wt% are percentages of a total weight of the collector.

According to some aspects, the froth flotation collector is in admixture with another collector selected from the group comprising or consisting of xanthates and dithiophosphate, or any mixtures thereof. The other collector may be a xanthate selected from the group comprising or consisting of isobutyl xanthate, sodium isopropyl xanthate and potassium amyl xanthate. In one aspect, the froth flotation collector is in admixture with said other collector and optionally one or more regulators selected from activators, frothers, depressants and/or pH regulators.

According to some aspects, the froth flotation collector comprises or consists of between 20 wt % to 90 wt% of said particles of lignin and between 10 wt % to 80 wt% of the other collector and optionally up to 100 wt% of one or more regulators selected from activators, frothers, depressants and/or pH regulators, wherein wt% are percentages of a total weight of the collector. In one aspect, froth flotation collector comprises between 30 wt % to 70 wt% of said particles of lignin and between 30 wt % to 70 wt% of the other collector, or between 40 wt % to 60 wt% of said particles of lignin and between 40 wt % to 60 wt% of the other collector, or about 50 wt % of said particles of lignin and about 50 wt % of the other collector. According to some aspects, the collector comprises or consists of between 20 and 90 wt% of the lignin collector as defined above, wherein wt% are percentages of a total weight of the collector in admixture with another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof. In one aspect, the collector comprises or consists of a mixture of between 20 and 90 wt% of the lignin collector as defined above in admixture with xanthate, or a xanthate selected from the group comprising or consisting of isobutyl xanthate, sodium isopropyl xanthate and potassium amyl xanthate, sodium isopropyl xanthate and potassium amyl xanthate. In another aspect, the lignin is isolated from lignocellulosic forest biomass, spruce or birch. In an aspect, the lignin is isolated from spruce or birch. In a further aspect, the other collector is isopropyl xanthate and/or potassium amyl xanthate and lignin is birch. In yet a further aspect, the other collector is isopropyl xanthate and/or potassium amyl xanthate, lignin is birch lignin or nanoparticles of birch, and the depressant is dextrans, starch, ferric chromium lignin sulfonate, modified (oxidised or aminomethylated) kraft lignin, carboxymethylcellulose or potassium chromium oxide. In yet a further aspect, the other collector is isopropyl xanthate and/or potassium amyl xanthate, lignin is lignocellulosic biomass, spruce or birch or nanoparticles thereof, and the depressant is dextrans, starch, ferric chromium lignin sulfonate, carboxymethylcellulose or potassium chromium oxide. In one aspect, the other collector is isopropyl xanthate and/or potassium amyl xanthate, lignin is birch or nanoparticles of birch, and the depressant is ferric chromium lignin sulfonate, carboxymethylcellulose or potassium chromium oxide. In yet another aspect, the other collector is isopropyl xanthate and/or potassium amyl xanthate, lignin is birch or nanoparticles of birch, and the depressant is ferric chromium lignin sulfonate or potassium chromium oxide. A froth flotation collector with a combination as defined in the paragraph is especially useful for separation of minerals copper, lead, and zinc from ores.

Tests show that lignin can be successfully used alone or alongside conventional froth flotation collectors, e.g. xanthates, depending on the treated ore. Depending on what conventional collector is mixed with the lignin, different wt-% of the lignin may be preferred. At some wt- %, the efficiency of the mixed collectors may be reduced or be equal compared to using only the conventional froth flotation collector. Since lignin is a much more environmentally friendly and cheaper material, it may be advantageous to use a mixture of lignin and one or more conventional collector even at reduced efficiency compared to using only conventional collectors. Through routine testing, the optimum weight percentage of lignin in the collector mixture may be determined to provide a froth flotation collector mixture having the advantages of lignin, while reducing the downside of less environmentally friendly conventional collectors. The desired wt-% may also depend on the particle size of the lignin particles and the type of/origin of the ore to be treated.

These froth flotation collectors are efficient in their respective applications. Tests have shown that a collector mixture comprising or consisting of lignin and xanthates (50:50 wt%) can be more efficient than the use of either collectors alone. As explained above, the efficiency of the collector must be put in relation to the fact that many froth flotation collectors are not environmentally friendly and have a negative impact on health and safety aspects. The flotation performance of the mixture is expected to be improved compared to using only xanthates as a collector. By mixing the lignin particles with other collectors, it is possible to provide an efficient froth flotation collector mix, which as a whole has a reduced environmental footprint with equal or almost equal flotation efficiency.

Lignin and any optionally other froth flotation collector are present in admixture with each other and do not chemically react with each other.

According to some aspects, said particles of lignin are isolated from lignocellulosic material. Lignocellulosic material is composed of cellulose, hemicellulose and lignin.

According to some aspects, the lignin is isolated from a lignocellulosic source/material, which may be herbaceous energy crops and/or short-rotation energy crops and/or short rotation wood crops. In one aspect, the lignin is isolated from spruce or birch. In another aspect, the lignin is microparticles or nanoparticles of spruce or birch. According to some aspects, lignin is isolated from any of wood or grass. According to some aspects, lignin is isolated from a lignocellulosic source. Extracting lignin from wood or grass is preferable since their content of lignin is high. Also, the extraction methods are especially efficient when extracting lignin from lignocellulosic sources. There is a wide range of lignin sources available, including for example wood, jute, hemp, cotton, herbaceous energy crops, short-rotation energy crops, short rotation wood crops, agricultural residues and grasses.

According to some aspects, the lignin is pure, chemically unmodified lignin. According to some aspects, the activator is selected from the group comprising or consisting of phosphates, silicates and carbonates. In one aspect, the froth flotation collector comprises or consists of lignin particles as defined above, an activator and a pH regulator. In another aspect, the froth flotation collector comprises or consists of lignin particles as defined above, an activator, a depressant and a pH regulator. In one aspect, the lignin is isolated from spruce or birch, the activator is a phosphate (Aerophine) and the pH regulator is lime or NaOH. In a further aspect, the lignin is isolated from birch, or microparticles of birch, the activator is phosphate (Aerophine), the pH regulator is lime or NaOH and the depressant is a lignin sulfonate, such as ferric chromium lignin sulfonate or modified (oxidised or aminomethylated)- kraft lignin or carboxymethylcellulose. In a further aspect, the lignin is isolated from birch, or microparticles of birch, the other collector is xanthate or iso-butyl xanthate and the activator is phosphate (Aerophine). In yet a further aspect, the lignin is isolated from birch, or microparticles of birch, the activator is phosphate (Aerophine), the pH regulator is lime or NaOH and the depressant is a lignin sulfonate, or carboxymethylcellulose. A froth flotation collector with a combination as defined in this paragraph is believed to be especially useful for separation of minerals nickel, iron and copper from sulphide ores.

According to some aspects, the depressant is selected from the group comprising or consisting of modified (oxidised or aminomethylated) kraft lignin, a lignin sulfonate, such as ferric chromium lignin sulfonate, carboxymethylcellulose, dextran, starch, and potassium chromium oxide and triethylenetetramine. According to some aspects, the depressant is selected from the group comprising or consisting of a lignin sulfonate, carboxymethylcellulose, dextran, starch, and potassium chromium oxide. In one aspect, the depressant is ferric chromium lignin sulfonate. In another aspect, the depressant is carboxymethylcellulose, starch or dextran. In an aspect, the depressant is carboxymethylcellulose. In a further aspect, lignin is isolated from birch or spruce, or microparticles of birch or spruce and the depressant is carboxymethylcellulose. In a further aspect, lignin is isolated from birch, or microparticles of birch and the depressant is carboxymethylcellulose. In yet a further aspect, lignin is isolated from birch, or microparticles of birch and the depressant is aminomethylated kraft lignin. A froth flotation collector with a combination as defined in this paragraph is believed to be especially useful for separation of minerals nickel, cobalt and copper from ores.

According to some aspects, the pH regulator is lime or sodium hydroxide. In one aspect, the pH regulator is sodium hydroxide. Such a froth flotation collector is believed to be especially useful for separation of copper from ores.

According to some aspects, the one or more mineral is selected from the group comprising or consisting of nickel, iron, copper, cobalt, lead and zinc.

According to another aspect, the aim is achieved by a method for producing the froth flotation collector according to the invention, as defined in method defined below. The method comprises or consists of isolating said particles of lignin from lignocellulosic material by a lignin isolation process selected from alkali extraction, a kraft process, organosolv fractionation and/or hydrolysis process.

According to some aspects, lignin is extracted from lignocellulosic material using organosolv method, especially organosolv fractionation method/process. Successful tests have been done using organosolv lignin having particles at a size of 5 pm or less as anionic froth flotation collector in froth flotation. With organosolv lignin is meant particles of lignin, which have been isolated from lignocellulosic material using an organosolv process.

The lignin's physical and chemical behaviour is different with respect to the original source and extraction method used. The above methods give lignin particles, which are advantageously used as a froth flotation collector.

The invention also relates to a use of the froth flotation collector according to the invention as a collector during froth flotation for separation of minerals, especially sulphide minerals.

In one aspect, the invention relates to a use of the froth flotation collector as defined anywhere above, as a collector for separation of minerals, such as sulphide minerals, from ores comprising or consisting of the steps of, i) grinding base ore material to a size that allows the minerals in the ore to be liberated, ii) providing a liquid mixture of said froth flotation collector, as defined anywhere herein, iii) mixing the grinded ore with the liquid in a container, iv) optionally adding further regulators selected from activators, frothers, depressants and/or pH regulators, v) rotating the container and supplying gas to the container, such that gas bubbles then float to the surface of the container and form a mineral rich froth, vi) remove the froth from the container.

In one aspect, the pH of the liquid in step ii) is between 9 and 11, or between 9.5 and 10.5, or between 9.3 and 9.7 or between 10.3 and 10.7, or about 9.5 or about 10.5. In another aspect, the froth flotation collector comprises or consists of a frother, at least 20 wt% lignin particles, which particles have a size of 5 pm or less. In yet another aspect, the froth flotation collector comprises or consists of a frother, at least 20 wt% lignin particles, which particles have a size of 5 pm or less, and between 10 and 80 wt% of another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof.

Brief description of the drawings

The invention will now be explained more closely by the description of different embodiments of the invention and with reference to the appended figures.

Fig. 1 shows a grade recovery curves for Cu, (A) Comparison of BM, BN and SM to IBX reference, (B) effect of pH with lime as pH modifier, (C) Substitution of lime by NaOH as a pH modifier, (D) Comparison of BM to IBX reference with addition of Aerophine. Fig. 2 shows grade recovery curves of Zn using the xanthate reference and xanthate-BN mixture.

Fig. 3 shows weight percentage recovery of Cu during flotation trials with xanthates and lignin particles.

Fig. 4 shows a SEM picture of microparticles of organosolv lignin.

Fig. 5 shows a recovery versus grade diagram using xanthates as a froth flotation collector and using lignin particles as a collector for recovery of copper.

Detailed description

Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The collector, uses and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein.

The terminology used herein is for the purpose of describing particular aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

As used herein "lignin" means a class of complex aromatic organic polymers that form key structural materials in the support tissues of vascular plants. Lignin forms covalent bonds to the polysaccharides of the wood and can crosslink them. Dominant structural components consisting of different phenylpropane units. Lignin is made up of three monomers, b-cumaryl alcohol, coniferyl alcohol and sinapyl alcohol. Lignin may originate from wood, agricultural residues, herbaceous energy crops or short-rotation energy crops or short-rotation woody crops.

As used herein "herbaceous energy crops" means plants with no or little woody tissue and grown for production of food or feed. Examples may be grasses, sugarcanes, corn, soybeans, wheat, barley, sunflower, rapeseed, and the like.

As used herein "short-rotation energy crops" means fast growing softwoods, such as pine, spruce and cedar or hardwoods, such as birch, poplar, willow and eucalyptus or herbaceous corps such as Miscanthus x giganteus and Pennisetum purpureum. As used herein "short- rotation woody crops" means fast growing hardwoods, such as poplar, willow, eucalyptus and the like.

As used herein "sulphide minerals" means minerals comprising one or more sulphide atoms.

Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

Froth flotation is a process for separating hydrophobic materials from hydrophilic, which process is used in the mining industry for recovery of valuable minerals, such as for instance copper, zinc, cobalt, nickel, iron and lead containing minerals. A froth flotation collector is a material that selectively binds to the surface of mineral particles and imparts hydrophobicity to the mineral particles, and thus enables separation of the mineral particles during the froth flotation.

A froth flotation collector is a type of reagent used in froth flotation for increasing the hydrophobic properties of the mineral particles to be separated. The mineral particles are usually very much larger than the particles of the collector. The particles of the collector connect to the surface of minerals. Air bubbles then connect to the hydrophobic part of the collector. If the surface coverage of the mineral particles by the collector particles is large enough, the mineral particles connect to the air bubbles and lift the mineral to the froth.

A froth flotation collector for use in froth flotation may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- optionally between 10 and 80 wt% of another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and b) one or more frother,

- optionally up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The invention also relates to a use of said froth flotation collector as defined herein for separation of one or more minerals, such as sulphide minerals from ores. The one or more minerals may be selected from the group comprising or consisting of copper, zinc, cobalt, nickel, iron and lead. Depending on the origin of the ore, other minerals and any combination of minerals may be separated. In an aspect, the minerals are selected from iron and copper.

The froth flotation collector or use thereof, may comprise or consist of at least 20 wt% lignin particles, which particles have a size of 5 pm or less, b) frother,

- optionally up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, b) frother, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, b) frother, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

In a further aspect, the froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of b) frother, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

At least 20 wt-% of the froth flotation collector consist of said particles of lignin, or at least 40 wt-% of the froth flotation collector consist of said particles of lignin, or at least 60 wt-% of the froth flotation collector consist of the particles of lignin at a size of 5 pm or less. Wt% are percentages of a total weight of the collector.

Figure 4 shows microparticles of organosolv lignin having sizes of less than 5pm. The lignin is adapted to be used as a collector in froth flotation. Since the lignin is relatively small, it can be efficiently distributed onto the surface of the mineral particles. The example lignin in figure 4 has been isolated from lignocellulosic wood material.

There are many conventional froth flotation collectors. The collector may comprise particles of lignin as defined anywhere above in admixture with one or more conventional froth flotation collector, such as xanthates, dithiophosphate, dithiocarbamate or any mixtures thereof. The other collector may be a xanthate selected from the group comprising or consisting of isobutyl xanthate, sodium isopropyl xanthate and potassium amyl xanthate. The froth flotation collector may be in admixture with said other collector and optionally one or more regulators selected from activators, frothers, depressants and/or pH regulators. These collectors are efficient collectors. Tests have shown that one effective froth flotation collector is a collector comprising or consisting of lignin alone or in combination with xanthates, for example at a ratio between 1 to 2 and 2 to 1, or about 1 to 1. Successful tests have been performed using a froth flotation collector comprising 50 wt-% of lignin particles at a size of 5 pm or less and 50 wt-% of PAX (Potassium Amyl Xanthate) in a CuPb-step of the flotation of CuPb-ore, and using a froth flotation collector comprising of 50 wt-% of lignin particle at a size of 5 pm or less and 50 wt-% of IBX (Iso bytul xanthate) in a Zn-step of the flotation of Zn-ore. Wt% are percentages of a total weight of the collector.

The froth flotation collector may comprise between 20 wt % to 90 wt% of said particles of lignin and between 10 wt % to 80 wt% of the other collector and optionally up to 100 wt% of one or more regulators selected from activators, frothers, depressants and/or pH regulators, wherein wt% are percentages of a total weight of the collector. The froth flotation collector may comprise between 30 wt % to 70 wt% of said particles of lignin and between 30 wt % to 70 wt% of the other collector, or between 40 wt % to 60 wt% of said particles of lignin and between 40 wt % to 60 wt% of the other collector, or about 50 wt % of said particles of lignin and about 50 wt % of the other collector. The froth flotation collector may comprise or consist of between 20 and 90 wt% of the lignin collector as defined above, wherein wt% are percentages of a total weight of the collector in admixture with another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof. The froth flotation collector may comprise a mixture of between 20 and 90 wt% of the lignin collector as defined above in admixture with xanthates.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less, between 10 and 80 wt% of another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and b) one or more frother,

- optionally up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- between 10 and 80 wt% of another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, b) frother, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- between 10 and 80 wt% of another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, b) frother, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- between 10 and 80 wt% of another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of a) activator, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- between 10 and 80 wt% of another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of b) frother, c) depressant, and d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The froth flotation collector or use thereof, may comprise or consist of

- at least 20 wt% lignin particles, which particles have a size of 5 pm or less,

- between 10 and 80 wt% of another collector selected from the group comprising or consisting of xanthates, dithiophosphate, and dithiocarbamate or any mixtures thereof, and

- up to 100 wt% of one or more regulators selected from the group comprising or consisting of d) pH regulator, and wherein wt% are percentages of a total weight of the froth flotation collector.

The other froth flotation collector may be xanthate, or a xanthate selected from the group comprising or consisting of isobutyl xanthate, sodium isopropyl xanthate and potassium amyl xanthate. The other froth flotation collector may be sodium isopropyl xanthate and potassium amyl xanthate. The other froth flotation collector may be isobutyl xanthate. The lignin may be isolated from spruce or birch. The froth flotation collector may comprise or consist of lignin isolated from birch lignin or nanoparticles of birch, sodium isopropyl xanthate and/or potassium amyl xanthate. The froth flotation collector may comprise or consist of lignin isolated from birch lignin or nanoparticles of birch, sodium isopropyl xanthate and/or potassium amyl xanthate, and ferric chromium lignin sulfonate, carboxymethylcellulose or potassium chromium oxide. The froth flotation collector may comprise or consist of lignin isolated from birch lignin or nanoparticles of birch, sodium isopropyl xanthate and/or potassium amyl xanthate, and ferric chromium lignin sulfonate or potassium chromium oxide. The froth flotation collector may comprise or consist of lignin isolated from birch lignin or nanoparticles of birch, isobutyl xanthate and/or potassium amyl xanthate, and ferric chromium lignin sulfonate. The froth flotation collector may comprise or consist of lignin isolated from birch lignin or nanoparticles of birch, isobutyl xanthate and/or potassium amyl xanthate, and lignin sulfonate and potassium chromium oxide.

The activator may be selected from the group comprising phosphates, silicates and carbonates. The froth flotation collector may comprise or consist of lignin particles as defined above, an activator and a pH regulator. The froth flotation collector may comprise or consist of lignin particles as defined above, an activator, a depressant and a pH regulator. The lignin may be isolated from spruce or birch, the activator may be Aerophine and the pH regulator may be lime or NaOH. The froth flotation collector may comprise or consist of lignin isolated from birch, or microparticles of birch, Aerophine and lime or NaOH and lignin sulfonate, such as ferric chromium lignin sulfonate or modified (oxidised or aminomethylated) kraft lignin or carboxymethylcellulose.

The depressant may be selected from the group potassium chromium oxide and triethylenetetramine. The depressant may be selected from the group comprising lignin sulfonate, modified (oxidised or aminomethylated) kraft lignin, carboxymethylcellulose, dextran, starch and potassium chromium oxide. The depressant may be ferric chromium lignin sulfonate. The depressant may be carboxymethylcellulose. The froth flotation collector may comprise or consist of lignin isolated from birch, or microparticles of birch and carboxymethylcellulose.

The pH regulator may be lime or sodium hydroxide. The pH regulator may be sodium hydroxide.

In addition to the components and combination of components of the froth flotation collector mentioned herein, generically or specifically, the froth flotation collector may in addition always contain one or more frothers and one or more pH regulators.

Lignin particle sizes may be measured by using SEM "Scanning Electron Microscopy". The picture of figure 4 is an SEM picture.

The method for producing the lignin may have an impact on how well the lignin works as a collector. The particles of lignin may be directly isolated from lignocellulosic material, for example, from organosolv treated lignocellulosic material. Lignocellulosic material is composed of cellulose, hemicellulose and lignin. The particles of lignin may be isolated from lignocellulosic material by any of alkali extraction, a kraft process, organosolv fractionation, and/or hydrolysis process. In some cases, an additional post-treatment process can be used.

The organosolv fractioning method may be as follows. Organosolv pretreatment involves the treatment of lignocellulosic biomass with mixtures of organic solvents and water for its fractionation into distinct streams at temperatures 160-210°C. During the process, solvents effectively solubilize lignin and hemicellulose from the lignocellulosic biomass, which are separated into the pretreating liquor. This method has environmental advantages. A catalyst may be added. The organosolv fractionation is a known method used in pulp and paper industry. Organosolv fractionation is, for example, described in Christos Nitsos, Ulrika Rova, and Paul Christakopoulos, "Organosolv Fractionation of Softwood Biomass for Biofuel and Biorefinery Applications", published 27 December 2017 in Energies-11-00050 by MDPI as well as in Petter Paulsen Thoresen, Leonidas Matsakas, Ulrika Rova and Paul Christakopoulos "Recent advances in organosolv fractionation: Towards biomass fractionation technology of the future", published 17 March 2020 in Bioresource Technology by Elsevier. Lignin fractionation may be performed by addition of water or by removal of the solvent in the pretreatment liquid after the organosolv method.

The ore to be treated in froth floatation is in general reduced to fine particles by crushing and grinding, a process known as comminution, so that the various minerals exist as physically separate grains. Chemical pre-treatment of ores is disclaimed. This process of liberation is performed before the froth floatation process. Depending on the sizes of the grains, as well as the type of ore to be treated, different particle sizes of the lignin may be used advantageous. For example, 50 wt-% of the particles of lignin may have a size of 1 pm or less, or at least 50 wt-% of the particles are nanoparticles having a size of 600 nm or less, or a size of 400 nm or less, or any combination thereof, wherein wt% are percentages of a total weight of the collector. There is a wide range of lignin sources available, including for example wood, grasses, and agricultural residues, or jute, hemp, cotton, and wood pulp. The lignin's physical and chemical behaviour may be different with respect to the original source and extraction method used. The above methods provide lignin particles which may advantageously be used as a froth flotation collector or in a mixture with one or more other collector. The lignin may be isolated/extracted from herbaceous energy crops and/or short-rotation energy crops and/or short-rotation woody crops. The lignin may be isolated/extracted from spruce or birch.

Lignin may be chemically modified. The lignin discussed herein is preferably pure lignin and not a derivate thereof. In other words, the lignin is preferably substantially chemically unmodified. Lignin particles may be nanoparticles or microparticles. The particles may be spherical. Lignin may be particles having a negative zeta-potential.

Use of the froth flotation collector as defined anywhere herein as a collector during froth flotation for separation of minerals, especially sulphide minerals from ores comprising or consisting of the steps of, i) grinding base ore material to a size that allows the minerals in the ore to be liberated, ii) providing a liquid mixture of said froth flotation collector as defined anywhere herein, iii) mixing the grinded ore with the liquid in a container, iv) v) optionally adding further regulators selected from activators, frothers, depressants and/or pH regulators, vi) rotating the container and supplying gas to the container, such that gas bubbles then float to the surface of the container and form a mineral rich froth, and vii) remove the froth from the container.

In step i) a rod mill with steel rods may be used as grinding material.

The pH of the liquid in step ii) may be between 9 and 11. The concentration of the collector in the liquid in step ii) may be between 1 to 15 g/ton (g/10 ³ kg) or 1 to 10 g/10 ³ kg.

The flotation time in step v) may be between 1 and 15 min, or between 1 and 10 min, or between 1 and 5 min.

Experimental

Experiments have been performed to compare the use of lignin particles equal or less than 5 pm in size with xanthates as a froth flotation collector in copper concentrating fractions. The experiments were carried out in flotation conditions optimized for xanthates. Figure 5 shows a recovery versus grade diagram showing the performance of lignin particle as a collector in comparison to xanthates. Table 1 shows the performance of lignin particle as a collector in comparison to xanthates. The recovery is the same for both collectors. The Cu grade is higher with xanthates as a collector, which results were expected since the flotation conditions where optimized for xanthates. Table 1: Accumulative weight percentage recovery of Cu during flotation trials with normal dose and 1.5x dose of lignin-based froth flotation collectors.

Normal doses were (g/lOOOkg ore): 2-2-1-5-5-5 for the different fractions. pH was adjusted to 10.5 prior to flotation and Nasfroth 350 (as a frother) was added during flotation.

Figure 3 shows weight percentage recovery of Cu during flotation trials with xanthates and lignin particles. The recovery was the same for xanthates and lignin particles.

The above discussed lignin is used in a collector for increasing hydrophobicity of ore during froth flotation.

Examples

Organosolv lignin is used as a froth flotation collector but the method is not limited to the use of organosolv lignin. The first step is a rougher flotation step. Rougher flotation comprises the step of adding pre-grinded base ore material into a mixer containing a liquid. The base material comprises different types of minerals and the goal is to separate some minerals from the base material. Small amounts of froth flotation collectors comprising lignin particles are added to the mixer. The mixer is adapted to stir the content so that the collector is mixed with the base material. Lime, or other pH regulator, is applied to adjust pH to a desired value. The content in the mixer is then moved to a container. Further regulators, such as activators and the like may then be added to the container.

The container is adapted to rotate the content and supply gas, typically air, to the content so that gas bubbles are formed. The gas bubbles then float to the surface of the container and form a froth. Some of the material made hydrophobic by the reagents attach to the gas bubbles and are lifted to the surface. At the surface, the air bubbles form a mineral rich froth, while leaving hydrophilic particles in the suspension. The froth is then removed from the container. In this step, the aim is to float materials comprising a larger concentration of desired materials, such as specific minerals or elements.

As another example, reversed flotation is used to float unwanted material to a greater extent and leave the desired material in the container. This can be used for example to remove impurities, such as sulphur. For example, the concentrated second material is moved to a new container, where similar steps are carried out in order to further float the desired materials from the base material. Optionally, further reagents may be added at the new containers.

In order to improve the recovery of the desired material, regulators and reagents may be added to increase the floating of the desired material. Large mineral particles often contain a mixture of different minerals in the same particle. These may still float because there is enough exposed surface of the floatable mineral. Regrinding of the larger particles is done to further liberate the valuable minerals from such particles. Further flotation steps are then needed to separate these and produce a cleaner final concentrate.

The flotation material is then moved through a sleeve, to separate large particles. The particles with a satisfactory size are then moved to a new flotation step, while the materials deemed too large is re-grinded. The concentrated desired material is then usually further floated, preferably at a pH adapted to float a specific material and to depress others, to further increase the concentration of the desired material.

The above froth flotation collector may be used in floatation processes in several fields; for example, mineral processing, wastewater treatment, and paper recycling, for example, to de ink papers.

Materials and methods

Table 2. Process protocol for the IBX reference ores A and B (Cu-Ni).

X, amount of lime required to adjust the pH; N, no pH adjustment

Ores were provided by Boliden Mineral AB. The Zn-Pb-Cu ore (0.4% Cu, 7.1% Zn, and 1.0% Pb) originated from the Kristineberg mine. (Boliden area, Sweden). Two different Cu-Ni ores were used, containing a mixture of chalcopyrite, sphalerite, and cobalt-pentlandite, and originated from the Kylylahti mine (Polvijarvi, Finland). The first is composed of 0.5% Cu, 0.3% Zn, 0.3% Ni, 12.3% Fe and 6.8% S (Ore A); whereas the second ore is composed of 0.4% Cu, 0.4% Zn, 0.3% Ni, 6.8% Fe and 3.1% S (Ore B). Micro- and nanoparticles were prepared from lignin extracted by organosolv pretreatment of birch and spruce wood chips, as previously described (Kalogiannis et al., 2018). Briefly, woodchips were treated at 183°C for 1 h in a 50% v/v (birch) or 60% v/v (spruce) ethanol in water solution. After organosolv, the lignin was dissolved in 75% v/v ethanol/water solution and homogenized using an APV-2000 homogenizer (SPX FLOW, Charlotte, NC, USA) at 750 bar (75 MPa) for 15 min. To isolate the lignin particles as a dry powder, ethanol was removed from the homogenized liquid followed by freeze drying, which yielded lignin microparticles (1-5 pm). For the preparation of nanoparticles (a size of less than 400-500 nm), the homogenized liquid was diluted two times and immediately freeze-dried (Matsakas et al., 2020). Nasfroth 350 frother and standard xanthate collectors, such as iso-butyl xanthate (IBX), sodium isopropyl xanthate (SIPX), and potassium amyl xanthate (PAX) were used in flotation trials (Table 2 for Cu-Ni ore A and B; Table 3 for Zn-Pb-Cu ore). The following were used as lignin- based collectors (at the same concentrations as xanthates): spruce lignin microparticles (SM), birch lignin microparticles (BM), birch lignin nanoparticles (BN), and birch lignin liquid (BL; derived directly after homogenization). Aerophine ^tm (sodium-diisobutyl dithiophosphinate (Solvay, Brussels, Belgium), ZnSC>4, CuSC>4, carboxymethylcellulose (CMC), and triethylenetetramine (TETA) were used as modifiers.

In a typical rougher flotation trial, 1 kg of crushed ore sample was milled in a rod mill (using 8 kg of steel rods as grinding media) with 1 liter of water for 40 min. The milled sample was then transferred to a 2.7-liter flotation cell (Outotec, Espoo, Finland) and water was added to fill the cell. The process protocol optimised for use of xanthates is summarized in Table 2 for ore A and ore B, and in Table 3 for Zn-Pb-Cu ore. The pH was adjusted by lime or NaOH. The flotation reagents (collector, frother, and regulators) were added and the flotation process was carried out in a two stage system (steps 2 -4 and 6-8) with three blocks of 2, 3 or 4 min in each. In total, seven fractions per flotation experiment were collected and the elements were analysed by X-ray fluorescence (Spectra Xepos Ametek, Kleve, Germany).

Process protocol for xanthate reference in Zn-Pb-Cu ore.

Table 3. Process protocol for xanthate reference in Zn-Pb-Cu ore.

X, amount of lime required to adjust the pH In the first set of experiments, SM, BM, and BN were compared to standard IBX reference in ore A (Cu-Ni). All experiments were carried out under the same conditions (Table 2). The tested lignin particles demonstrated high selectivity towards Cu flotation, with total Cu recovery of 87%, 70%, and 77%, and the highest grades reaching 8.9%, 8.6%, and 7.9% for SM, BM, and BN, respectively. In comparison, the xanthate reference achieved up to 92% recovery and a grade of 9.2% (Fig. 1A). In all cases when lignin particles were used as a collector, total Fe recovery remained below 15%, whereas for xanthates it was 91%.

To narrow the amount of experiments, flotation conditions were improved using BM as a collector. First, the effect of pH was examined and the initial pH was set to 9.5 instead of 10.5 by lime (Fig. IB). This change resulted in a considerable increase in Cu recovery from 70% to 82%, with the highest grades rising from 8.6% to 9.0%. In addition, 62% of Cu was recovered in the first stage, while when the pH was set at 10.5, majority of Cu (57%) was recovered in the second stage (with the recovery in the first stage to be 13%). Subsequently, in the next trial, lime was replaced by NaOH as a means to correct the pH (pH was set at 10.5), and a significant improvement was observed in the total recovery, which reached 82% (58% in the first stage) and the grade, which reached to 9.6% (Fig. 1C).

Next, the effect of dosage, a crucial parameter, was studied. A BM dose increase of 1.5-times led to no significant change in recovery or grades, suggesting that the current dosage was sufficient for the flotation process.

Finally, addition of an activator (Aerophine ^® ) to improve the flotation of Ni, which did not float with any lignin particles, was assessed. This combination provided better results than the initial xanthate reference. Total recovery of Cu and Ni improved to 97% and 92%, with grades of 9.9% and 2.5%, respectively, when BM was used as a collector. While the grade for Cu was similar to that obtained with the xanthate reference, the grade for Ni was 2.5-times higher with BM. Addition of activator to the xanthate reference (Fig. ID) resulted in a total Cu and Ni recovery of 96% and 94%, with 16.6% better Cu grade and 1.5-times higher Ni grade compared to xanthate alone. However, use of Aerophine ^® with lignin promoted Fe flotation, even though total Fe recovery was lower (82%) compared to that with xanthate (91%).

Whereas data about organosolv lignin (or any other type of technical lignin) use as a collector in the mineral froth flotation are not available yet, studies about sulfonate utilization as a gangue depressants have been reported (Booth and Pickens, 1949). The depressants are added to the mineral froth flotation in addition to collectors to improve the selectivity and recoveries of the target minerals. Booth and Pickens (1949) patented the use of lignin sulfonates as depressants in froth flotation of copper sulphide ores as a mean to improve Cu recoveries and minimisation of the loss of Cu in tailings. The optimal amount of lignin sulfonates in the feed should be between 4.5 and 136.0 g/1000 kg. Timoshenko et al. (2011) have used four modified kraft lignins as a depressant in the flotation of disseminated Cu-Ni ores. The best result when supplementing with aminomethylated modified kraft lignin was recoveries of 58.1% and 33.0% with grades of 10.5% and 5.0% for Cu and Ni, respectively, compared to use of CMC as depressant, where 53.1% and 31.13% with grades of 10.0% and 5.2%, respectively, were reached (Timoshenko et al., 2011).

Cu-Ni ore B

The second set of experiments was carried out with ore B (Cu-Ni), which contains mainly Cu, Ni, Co, as the valuable elements. Given its similar mineral composition to ore A, ore B was used to verify the results described above. Two types of xanthates were used as a reference (IBX and SIPX), with SIPX providing slightly better results than IBX. The recovery of Cu, Ni, Co, and Fe was 96%, 90%, 80%, and 58%, respectively, when SIPX was used as a collector and grades were up to 13.5%, 3.5%, 0.3%, and 44.9%. The use of IBX resulted in recoveries of 93%, 87%, 79%, and 66%, and grades of up to 13.9%, 2.6%, 0.2%, and 37.6%, for Cu, Ni, Co, and Fe, respectively.

Experiments were carried out with BM and the high selectivity towards Cu was confirmed. Specifically, Cu recovery was 74% and grade was up to 5.4% with BM at an initial pH of 10.5. The lower pH of 9.5 adjusted with lime had a similar effect on ore B as on ore A. Despite a slightly lower total Cu recovery of 65% and grade of 5.1%, a higher Cu recovery (50%) in the first stage was confirmed. Moreover, total Fe recovery did not exceed 19%, when BM was used. Subsequently, the CMC depressant was added to BM at pH 9.5 to reduce Si flotation, which tended to have high grades in previous experiments. The resulting Cu recovery remained as high as 74%, but the recovery of Ni and Co increased to 68% and 38%, respectively, compared to flotation without CMC (12% and 9%). In addition, grades of up to 7.9% (Cu), 2.4% (Ni), and 0.1% (Co) were achieved. The total Fe recovery also increased to 58% at pH 9.5 with addition of CMC, however the recovery was still lower compared to the IBX reference (66%).

Zn-Pb-Cu ore

The third set of trials was carried out with Zn-Pb-Cu ore to study the recovery of Pb, Zn, and Cu. BM, BN, and BL were examined and compared to the xanthate reference (Table 3). Recoveries of Cu, Pb, and Zn obtained with the xanthate reference were 84%, 70%, and 96%, with grades up to 9.1%, 20.6%, and 44.7%, respectively. The selectivity of BM and BN shifted from Cu to Pb; however, total Pb recovery did not exceed 12%. The use of BL resulted in recoveries of Cu, Pb, and Zn were 67%, 73%, and 47%, with grades up to 1.8%, 6.2%, and 9.5%, respectively.

Finally, a mixture (1:1) of xanthate and lignin (BN) improved total recovery of Cu, Pb, and Zn to 91%, 85%, and 98%, while grades of up to 5.5%, 13.4%, and 45.5%, respectively, were achieved. The most significant improvement concerned an increase in Zn recovery and grades (Fig. 2). In addition, 88.8% of Zn was recovered into Zn concentrate and only 9.4% into Cu-Pb concentrate, when a mixture of xanthate and BN was used compared to 69.7% of Zn in Zn concentrate and 26.7% of Zn in Cu-Pb concentrate, when xanthates were used. Thus, lignin collectors could effectively replace 50% of xanthates during flotation, thereby lowering the need for fossil-based xanthates. Moreover, as a biodegradable source of carbon, lignin could foster the degradation of other organic pollutants (Abaecherli and Popa, 2005) if lignin is released into the environment. When ferric chromium lignin sulfonate was used for Cu-Pb-Zn ore separation as a depressant, the Pb recovery and grade was improved. Moreover, 83.3% of Pb recovery was in the Pb concentrates and only 4.7% in Cu concentrates, when lignin sulfonate was use compared to flotation with K2Cr2C>4, when only 77.9% of Pb was in the Pb concentrate but 10.7% was in the Cu concentrate (Yu et al., 2018).

Conclusion

This study shows for the first time that lignin nanoparticles can be used as flotation collectors in mining applications. Total Cu recovery of 70-87% and grade of 7.9-8.9% were achieved in rougher flotation tests using lignin collectors in ore A. In addition, BM outperformed xanthate.

The present invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims.