A considerable art has been developed to separate minerals from associated gangue using air bubbles. Typically a collecting reagent, such as sodium ethylxanthate, is added to an aqueous suspension of a mineral, for example chalcopyrite containing a silica gangue. The ethylxanthate ions are preferentially adsorbed by the chalcopyrite. If small air bubbles are then made to contact both silica and chalcopyrite particles, only the chalcopyrite particles adhere and they can then be floated to the surface of the suspension and separated by skimming the surface. The air bubbles are attached to the mineral by the surface tension developed in the ring where the-mineral protrudes into the air bubbles. The air bubbles have buoyancy which counteracts the gravitational force on the particles of mineral thus allowing flotation to occur. In many instances the bubbles must be stabilised with frothing agents to maintain the bubble with particles on the surface for sufficient time to permit skimming of the floated mineral particles.

The alkyl-, aryl-and alkylaryl-substituted hydroxamic acids and salts have been proposed as flotation collection agents for froth flotation of non-sulfidic mineral species. While the hydroxamates are not known to have achieved any significant commercial use as flotation collection agents, attention is drawn to U. S. patents 4,324,654 to Rule and 4,629,556 to Yoon et al ; 4,871,466 and 4,929,343 both to Wang et al ; and 5,126,038 to Nagaraj.

In USP 4,324,654 to Rule, there is disclosed a method for recovery of copper from ores containing this metal as the non-sulfide mineral atacamite/paratacamite [Cu2 (OH) 3CI], using an aromatic or fatty alkyl hydroxamate for the flotation of that mineral. This disclosure of Rule confirms that aromatic or fatty alkyl hydroxamates are not effective for the froth flotation

of sulfide minerals and, to maximise recovery of copper, the teaching is to use the hydroxamate in combination with a xanthate, to achieve flotation of copper sulfides present simultaneously with the atacamite/paratacamite.

U. S. patents 4,871,466 and 4,929,343 relate respectively to a flotation collector agent based on a fatty hydroxamic acid or an alkali metal salt of such acid, and to the use of such agent in the froth flotation of non-sulfide minerals, preferably clay. These teachings tends to support the lack of utility of aromatic and fatty hydroxamates alone in the flotation of sulfide minerals. U. S. patent 5,126,038 similarly proposes the use of hydroxamate acids or their salts for the beneficiation of precious metals from sulfide ores containing pyrite and pyrrhotite. The hydroxamate preferably is used in combination with standard sulfide collectors such as xanthates, while the overall disclosure indicates utility of the hydroxamates, when used alone, only for flotation of precious metals from the sulfides rather than for flotation of the sulfides.

We have now found in accordance with the invention that minerals, including mineral sulfides, may be concentrated by using a solid particulate separating agent which includes hydroxamate functional groups at the surface thereof.

Summary of the invention / Accordingly the invention provides a collector for mineral suspension comprising a solid particulate material having a surface provided with hydroxamate functional groups.

The solid particulate material preferably has a property which allows it to be selectively collected from gangue. Preferably the solid particulate material is magnetic, buoyant in aqueous liquid or magnetic and buoyant.

Examples of suitable magnetic particulate materials include magnetite, haematite, ilmenite and the ferrites.

Examples of suitable buoyant materials include synthetic organic particulates such as spheres. Such particulates may be buoyant by virtue of being porous or hollow.

Synthetic organic spheres are known for use as density reducing agents for constructions of bought articles such as shipping buoys, boat hulls and as fillers in plastic materials and in thermal installation.

Preferably the particles are of size in the range of from 50 to 800 microns preferably 100 to 500 microns.

In a further aspect the invention provides a method for upgrading gangue associated mineral in particulate form comprising the steps of providing a solid particulate material comprising hydroxamate functional groups at the surface thereof; contacting the gangue associated mineral with the particulate material in an aqueous liquid whereby the minerals become attached to the hydroxamate functional groups on the surface of the particles ; and separating the particulates with attached mineral particles from the gangue.

In the preferred embodiments the particulate materials are either buoyant, magnetic particles or both buoyant and magnetic.

In another aspect the invention provides a process for the preparation of particulate material for upgrading minerals comprising providing a particulate substrate which is buoyant, magnetic or both buoyant and magnetic and comprises functional groups reactive with hydroxylamine to form hydroxamate functional groups; reacting the surface of the substrate with hydroxylamine to provide hydroxamate functional groups at the surface.

The hydroxamate functional groups may be present in the form of the hydroxamic acid or salt thereof such as the alkali metal, ammonium or alkaline

earth metal salt. The acid form, sodium salt, potassium salt and mixtures thereof are preferred.

Detailed Description of the Invention The first aspect of the invention provides a solid particle which may and typically will be buoyant or magnetic and which has hydroxamate functional groups provided at the surface. The hydroxamate functional groups are preferably bonded to the surface of the particle and most preferably covalently bonded.

We have found that the solid particles may be used to separate minerals by binding with the surface hydroxamate functional groups which provide effective chelation of mineral values. The magnetic or buoyant properties may be used to facilitate collection of the associated minerals.

The substrate used in the invention is preferably provided with surface functional groups capable of reacting with hydroxylamine to form hydroxamate functional groups. Examples of such groups include carboxylic acid groups, acid chloride groups, acid anhydride groups, esters such as (Ci-Ce lower alkyl) ester groups, nitrile, amide and suitable carboxylic acid derivatives.

The functional groups capable of reacting with hydroxylamine may be part of the composition of the substrate. For example in one embodiment of the invention the substrate comprises synthetic organic polymer particles such as microspheres which include monomeric units capable of reacting with hydroxylamine.

Examples of suitable monomeric units include acrylic acid, methacrylic acid, esters of acrylic acid such as (Ci to C4 alkyl) esters, esters of methacrylic acid such as the Ci to C4 alkyl) esters, acrylamide, acrylonitrile and mixtures thereof.

Acrylic acid, methacrylic acid and their esters are particularly preferred.

Synthetic organic polymer particles may and typically will comprise an inert monomer, that is a monomer which is not reactive with hydroxylamine and is

typically hydrophobic. Examples of suitable inert monomers include styrene, vinyl chloride, vinylidene chloride and olefinic monomers.

Synthetic organic polymer spheres may (and it is typically preferred that they do) include a cross-linking monomer such as divinyl benzene to confer an appropriate rigidity having regard to the function which they are to perform in mineral separation.

Suitable monomer compositions will be readily apparent to those skilled person in accordance with the functions described herein. A particularly preferred monomer composition includes 2 to 98% w/w of monomer capable of reacting with hydroxylamine to form hydroxamate functional groups and 2 to 25% w/w crosslinking agent. The compositions may and preferably will contain at least 50% w/w of inert monomer such as styrene.

If desired the synthetic polymeric substrate may incorporate magnetic particles to enable it to be isolated by magnetic means.

In a further embodiment of the invention the substrate is provided with said functional groups capable of reacting with hydroxylamine to form a hydroxamate group by a surface modification process. The surface of the particles may, for example, be modified by coating with a coating composition comprising said functional groups. For example, suitable coating compositions may include monomer such as acrylic acid, acrylic acid esters such as Ci to C4 alkyl esters, methacrylic acid, methacrylic acid esters such as (Ci to C4 alkyl esters), acrylonitrile, acylamide and mixtures thereof. Such monomers may be applied in a coating composition with suitable inert monomers.

In a particularly preferred embodiment the surface of the substrate is treated with organofunctional silane or siloxane and a monomer having said functional groups. Preferably the silane or siloxane includes one or more amine functional groups which undergo Michael reaction with the monomer comprising said functional groups. In this embodiment the organofunctional silane or siloxane may be reacted with the monomer to form a Michael adduct prior to applying a

coating to the substrate or the substrate may first be treated with the organofunctional silane or siloxane.

When the monomer is an acrylonitrile group the silane may react therewith to form an amido-oxime group which will, in the presence of water, form hydroxamate functional groups.

This surface treatment step may also be used to provide hydroxamate functional groups at the surface of ceramic or borosilicate microspheres.

The organosilane may be an alkyl silane or functionalised alkyl silane particularly a primary or secondary amino substituted alkyl silane.

Organosilanes of the type used in the present invention are known as coupling agent.

When the particulate substrate is a synthetic polymeric material the organosilane and optionally the hydroxamate may be incorporated into the particle during the polymerisation process.

The hydroxamate groups may be formed by reaction of said functional groups with hydroxylamine free base or similar agent. Methods for hydroxamation may be chosen from these listed in International Application PCT/AU01/00920. The contents of which are herein incorporated by reference.

In a second aspect, the present invention also provides a process for upgrading and concentrating metals and minerals from a wide range of ore types and other materials. The process of the invention can be used for the upgrading and concentrating metals and minerals, for example, from: (a) sulfide base metal ores-as sulfide material or as oxidised in situ (wet) or pre-roasted in air (to achieve surface oxidation only) ; (b) oxidised sulfide ores, for example, supergene, gossans and/or weathered deposits; (c) oxide, carbonate, silicate and/or hydroxy base metal ores;

(d) metallic ores, for example, copper, silver, gold and platinum ores as metal, or as alloys or intermetallics such as with tellurium, arsenic, selenium and/or sulfide ; (e) base metal tailing ; fine or ultrafine oxide ores, or sulfide ores where oxidation to some extent will occur due to fine grinding; and (g) oxide ores of large ion lithophile metals, for example, uranium, vanadium, aluminium, calcium, thorium, tungsten, strontium, barium, zirconium, hafnium, beryllium and/or titanium.

The method of the invention may use a process similar to that disclosed in U. S. patent 4,657,666 to Snook et al. Particles of a mineral or metal are contacted, in a liquid medium, with particles of a magnetic material having hydroxamate functional groups at the surface and the particles of the mineral or metal with attached magnetic particles are separated from gangue and other mineral species by application of a magnetic field. In a further alternative, particles of a mineral or metal are contacted, in a liquid medium, with buoyant particles having hydroxamate functional groups at the surface such as modified hollow mineral spheres or plastic composites, and the mineral or metal particles are floated under the action of buoyancy of attached buoyant particles.

While the process of the invention can be used with a wide range of ore types and other materials, the process differs depending on whether or not sulfide species are present and to be recovered by the flotation. The options available include the following: Where the material to be treated includes sulfide minerals, the options available can vary with whether these are to be upgraded or concentrated, whether there are non-sulfidic minerals present and whether non-sulfidic minerals are or are not also to be upgraded or concentrated. In a first form of the process of the invention, with only non-sulfidic minerals present and to be recovered, hydroxamate functionalised particulates can be used as a flotation collection agent for this. In a second form of the process of the invention, for simultaneous recovery of sulfide minerals and non-sulfidic minerals, the

hydroxamate flotation collection agent, can be used in combination with a conventional flotation collection agent for sulfide minerals, such as a xanthate.

However, in a third preferred form of the process, again for simultaneous recovery of sulfide and non-sulfidic minerals, the material to be treated is subjected to a pre-treatment to achieve surface modification of the sulfide minerals which enables use of hydroxamate alone as the sole flotation collection agent for the simultaneous recovery. That is, the need for use of a conventional sulfide flotation collection agent is obviated. However, a conventional agent such as a xanthate still can be used in combination with the hydroxamate, if required, such as where the surface modification is used selectively to effect only one or some of mixed sulfide minerals. Where a conventional agent is used in combination with the hydroxamate, functionalised particles, the quantity of it that is required is reduced relative to the situation in the second form of the process, as it is required only for recovery of the sulfide minerals which are not subject to surface modification. In the third form of the process, the hydroxamate most preferably is a flotation collection agent, although an active commercial form of xanthate can be used if required.

With non-sulfidic materials, including those having oxidised sulfide minerals, those free of sulfide minerals to be recovered and other materials such as base metal tailings, the hydroxamate most preferably is a flotation collection agent according to the first aspect of the invention.

The pretreatment of sulfide minerals, where required in the method of the second aspect of the invention, entails surface oxidation of the sulfide minerals.

The surface oxidation need be not more than is necessary to provide surface oxide on particles of the sulfide minerals sufficient to enable the hydroxamate flotation collection agent to act on those particles as if comprising non-sulfidic particles. The extent of the surface modification can vary with the fineness to which the material is ground and with the extent of liberation of the sulfide minerals to be covered. However, in general, it is found that surface oxidation of the sulfide minerals to about 5 to 10 monolayers is sufficient to enable the hydroxamate collection agent to exhibit flotation reactivity with respect to the surface oxidised sulfide mineral particles.

The surface modification can be achieved by controlled roasting of dry or substantially dry sulfide mineral containing material in an oxidising atmosphere, such as air. However it is found that control desirable in limiting oxidation to only a surface depth of about 5 to 10 monolayers is best achieved in a liquid medium, such as water. With the surface modification effected in a liquid medium, a variety of oxidising agents can be used. A preferred agent includes ozone enriched air having, for example, from about 2 to 5 volume percent ozone. The ozone enriched air preferably is bubbled through a slurry of the sulfide containing material, for a period and at a rate sufficient to achieve the required modification by oxidation of the surface of sulfide mineral particles.

The ozone enriched air may, for example, be bubbled at a rate of from 20 to 50 ml per minute per kilo of solids in the slurry such as for a period of up to about 15 minutes, but preferably for from 6 to 8 minutes. The slurry preferably is agitated during the modification treatment with ozone in order to maximise the uniformity of exposure of the sulfide particles to the oxidising action of the ozone enriched air.

Other oxidising agents suitable for pretreatment of sulfide minerals in a liquid medium include hydrogen peroxide and metal peroxides and superoxides. The metal peroxides and superoxides most preferably are those of the alkali and alkaline earth metals, with the compounds of sodium and potassium being most preferred.

As indicated, conducting the surface oxidation of particles of sulfide materials in a liquid medium enables more precise control over the surface oxidation. This is because the concentration and rate of addition of the oxidising agent can be closely controlled and monitored while, relative to at least some roasting methods, oxidation in a liquid medium enables more accurate control over residence or reaction time. However oxidation in a liquid medium has a further significant advantage. This is the ability to retain the mineral containing material, to be subjected to flotation, in a liquid medium during each of the grinding, oxidation pretreatment and actual flotation stages.

In general, it is desirable not to give rise to flotation of iron-containing minerals such as pyrite and arsenopyrite. This can be achieved by use of the hydroxamate as flotation collection agent without use of a conventional sulfide mineral collection agent, if the surface modifying oxidation pretreatment is appropriately controlled. For this, the surface oxidation is controlled, by control over the concentration and/or rate and duration of addition of oxidising agent so as to achieve selective surface oxidation of sulfide minerals other than those containing iron. The iron-containing minerals generally require more strongly oxidising conditions than non-iron-containing minerals in order for their particle surfaces to be oxidised, and such conditions can relatively readily be avoided if oxidation of non-iron-containing sulfide minerals is limited to surface oxidation to the extent of about 5 to 10 monolayers.

At least in some forms of the process of the invention, the invention allows use as flotation collection agent of a combination of hydroxamate functionalised particles with a conventional xanthate. This principally is where minerals to be recovered by flotation include sulfides and non-sulfidic minerals. However, as also indicated, an alternative is to subject the sulfide minerals to a pretreatment to achieve surfactant oxidation, prior to use of hydroxamate functionalised particles alone as the collection agent. Of these alternatives, the latter can be more beneficial, since the hydroxamate functionalised alone enables greater selectivity in the minerals recoverably by flotation, relative to xanthates. This, at least in part, is due to selectivity possible in conducting the pretreatment.

However, as a further alternative to use of the combined collection agent, the hydroxamate functionalised particulates and other agent, such as a xanthate, can be used in respective flotation stages.

Magnetic flotation as disclosed in U. S. patent 4,657,666 to Snook et al may be carried out using the hydroxamate modified particles of the invention.

In the case of magnetic flotation, the process of the invention resembles the art of flotation but uses hydrophobic magnetic particles instead of air bubbles as the separating medium. The invention also aims to provide a method of mineral concentration which represents an improvement over the use of air bubbles. In

that case, a gangue-associated mineral having a hydrophobic surfaces, and in particulate form, is contacted with particles of a magnetic material also having hydrophobic surfaces, whereby the mineral particles become attached to the surface of the magnetic particles. The magnetic particles with the attached mineral particles are separated from the gangue by magnetic means, and the mineral particles are then detached from the magnetic particles. As in the disclosure of U. S. patent No. 4,657,666, the magnetic mineral (for example, magnetite) is silanised and the silanised particles functionalised using hydroxylamine to produce hydroxamate functional groups at the surface of the particles. Contact of the mineral to the magnetic particles may be carried out by mixing the particles in a fluid, preferably aqueous liquid, suspension, or the particles may be mixed together in the dry state.

Separation of the mixed mineral/magnetic particles from the gangue and separation of the magnetic particles from the mineral particles after detachment may be achieved by any suitable magnetic separation apparatus of conventional or specifically-designed type. The concentrated mineral particles may be detached from the magnetic particles by any suitable magnetic separation method. For example, the flotation reagent may be destroyed with oxidising reagents such as hypochlorite, hydrogen peroxide or air, or by pyrolitic degradation. Alternatively, the flotation reagent may be displaced by ions such as cyanide or hydroxide. Detachment may also be achieved mechanically, by violent agitation, for example, that caused by intense oscillating magnetic field.

The optimum size for the magnetic particles for any particular application will be best determined by experiment. Generally the magnetic particles should be at least comparable in size with the mineral particles and preferably somewhat larger. We have found that for most applications involving mineral particles of 100 mesh BSS or smaller magnetic particles of-60 to +100 mesh are most suitable.

In the magnetic separation form of the present invention the surface of the magnetic material is further modified to chemically attach the hydroxamate flotation collection agent such that molecules of the agent protrude from the

surface. The target mineral particles are then able to be strongly attracted to the hydrophobic solid particle surface by surface tension forces and the considerable van der Waals force, with mineral selectivity provided by the hydroxamate collection agent. Further reagent may be provided by addition of the hydroxamate or other surface modifying agents to the slurry liquid phase.

Mineral micelles are then formed between the modified magnetic particles and the target mineral or minerals. The separate selectivity is considerably enhanced for oxidised target minerals, including sulfide minerals subjected to the surface modification of the present invention, by the presence of the hydroxamate flotation collection agent on the magnetic particle surface.

The combined forces of attraction between magnetic, modified particles and mineral particles enable larger mineral particles to be separated more reliably.

When very fine mineral particles are floated, the hydrophobic surfaces exert a powerful force on micelles of minerals by spreading them over the active surface. The effect can be increased by using magnetic particles with indented surfaces that allow a greater area of contact and an increased resolved surface tension force towards the magnetic particles. Also, the energy required to separate a magnetic particle using a conventional magnetic separator is much less than the energy required to compress air to make bubbles and then skim the surface. Moreover, the magnetic flotation does not require frothing reagents, which constitute roughly ten per cent of the cost of running a conventional flotation process.

In the case of differential density or buoyancy flotation, the process of the invention resembles the procedure for magnetic flotation but uses chemically modified surfaces of water buoyant particles for collection, rather than magnetic particles. The buoyant particles consist most preferably either of a hollow, ceramic mineral or synthetic material, or a solid or porous material with a density of less than 1, for example a plastic material of suitable density.

The spheres may be formed of borosilicates and microspheres of this type are conventionally used as fillers in plastics for density reduction. Synthetic organic microspheres may be formed of acrylic, poly (vinyl chloride), polystyrene

phenolic resins, polyvinylidene chloride, polymethylmethacrylate, polyolefins and polyvinyl acetate. Polymers and copolymers of one or more of acrylic acid and methacrylic acid are preferred. The use of a cross-linking comonomer such as divinyl benzene is preferred.

The buoyant particles are modified as for magnetic particles to produce hydrophobic surfaces from which molecules of the hydroxamate flotation collection agent protrude to achieve selective collection of oxidised target minerals and capture of them in the form of micelles. After mixing such that the collection of target minerals occurs, agitation to achieve mixing is greatly lessened to allow the buoyant particle micelles to float to the surface and be removed. The target mineral can then be separated from the buoyant particles, and the latter then recycled, as in the magnetic flotation methodology.

In the case of preparation of magnetic particles made sufficiently hydrophobic by the hydroxamate flotation collection agent, all of the principal, currently known magnetic materials can be made hydrophobic. In general, the magnetic oxide materials such as magnetite, hematite, ilmenite, and the ferrites, can be activated by either concentrated acid alkali to give a surface rich in hydroxyl radicals that can be used to attach silanes or siloxane and other organic reagents by methods known per se to produce hydrophobic surfaces. The silane or siloxane may be selected from the group consisting of optionally substituted alkyl silanes and optionally substituted alkyl siloxanes primary and secondary amines substituted alkyl silanes are generally preferred. Magnetic metals such as iron, nickel, cobalt and their alloys, for example alloys of rare- earth elements and cobalt, can be made hydrophobic by producing either hydroxyl-rich surfaces in weak alkaline solutions or by generating a thin glass layer on their surface and then further treating the surface with alkyl silanes, alkyl siloxanes and like organic reagents.

The magnetic particles can then be further surface modified by incorporation of hydroxylamine with the silanising agent to form a hydrophobic, hydroxamate- coated surface.

The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention.

In order that the invention may more readily be understood, description now is directed to the following Examples.

Example 1 A quantity of base metal tailings containing copper and zinc was ground to 80 per cent less than 75 lim and respective samples were subjected to treatment with the magnetic flotation and the differential density flotation methods.

(a) Magnetic flotation A sample of magnetite was screened and the size range 50 to 250 ; j. m retained for silanising. The surface was cleaned with 1% sodium EDTA, which was adjusted to pH 10 with ammonia, then washed with distilled water. The magnetite was dried at 100°C and, when cool, a sample was stirred into a 1% solution of Dow Corning Z-6020 silane (N-beta-aminoethyl-gamma- aminopropyltrimethoxysilane). The silanized magnetite was treated with methylmethacrylate (5% in hexane) to provide Michael addition with the amine silane. The particles were washed with hexane. Hydroxylamine (5% in methyl alcohol) was added with potassium hydroxide (1% aqueous solution) and then decanted to remove excess reagent. The reaction mixture formed potassium hydroxamate coated surfaces on the magnetic particles. The reaction was completed by drying the treated magnetite at 100°C for two hours.

A sample of the dry, crushed tailings were slurried into water and the pH was adjusted to between 8.0 and 8.5 with lime at a ratio of 10g of tailings to 100 ml of water. Hydroxamate-treated magnetite particles were added to the slurry at a solids ratio of 2 parts tailings to one part treated magnetite, and the slurry then was mixed by gentle stirring for 15 minutes. Magnetite/mineral micelles then were recovered magnetically by being drawn upwards out of the slurry mixture, and then washed carefully with water. The mineral concentrate was recovered by treatment with 50 volume percent hydrogen peroxide solution for 10 minutes,

followed by agitation and the magnetic removal of the magnetite, leaving the mineral product which was dried and analysed. Analysis. showed a 5.5: 1 concentration of copper and a 4.1: 1 concentration of zinc from the tailings to the concentrate.

(b) Differential Density Flotation A second sample of the tailings described in Example 1 were similarly treated with buoyant hydroxamate treated plastic particles of part (a) of the example. In this case an ultrasonic bath was used (for 15 minutes) to separate the mineral concentrate from the buoyant plastic material. Analysis of the product showed a 6.5: 1 concentration of copper and a 5.2: 1 concentration of zinc from the tailings to the concentrate.

In each case, treatment of the ore sample with hydrogen peroxide facilitated recovery of both sulfidic and oxide constituents of the copper, along with the zinc oxide, present in the tailing.

Example 2-Buoyant Particle Flotation Buoyant particles may be formed from a monomer composition comprising styrene (about 80% w/w) methyl methacrylate (15% w/w) and divinyl benzene (about 5% w/w). Buoyant copolymer particles of size in the range of 100 to 500 microns may be modified to form hydroxamate groups at the surface by reaction with hydroxylamine. The reaction with hydroxylamine was conducted in potassium hydroxamate 1% solution and the resulting potassium hydroxamate coated product was washed and dried.

Example 3 (a) Buoyant, synthetic, organic spheres of a nominal, but not exclusive, size range of 100 to 500 pm, and having a solid, porous or hollow nature can be prepared by known procedures. A suitable preparation uses the combination of acrylate and divinyl benzene which are co-polymerised to form cross-linked, water- stable particles. During the co-polymerisation the particles can be made hydrophobic by the addition of a silanising agent such as Dow Corning Z-6020 silane. The particle surface is then derivatised by conversion to a hydroxamate following the addition of hydroxylamine.