TECHNICAL FIELD

This invention relates to a composite material made of zeolite and biochar. More particularly the invention is described with reference to the composition, preparation and uses of such composite material.

BACKGROUND

Biochar (char) is a charcoal typically used as a soil amendment, namely as a soil improver or conditioner. Like most charcoal, biochar is made from biomass, such as wood for example, via pyrolysis. Biochar is defined by the International Biochar Initiative as "The solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment". It has been known for many years, and its history and uses as fertiliser are set out in the “Background of Invention” of WO 2012/092962 (Leger) entitled“Method of preparing a carrier comprising a microporous material”. Independently, biochar can increase soil fertility of acidic soils (low pH soils), increase agricultural productivity, and provide protection against some foliar and soil-borne diseases. Whilst biochar’s properties may vary based on the biomass material from which it is derived, biochar typically has a high“specific surface area” which results in it being well suited for“adsorption” namely the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. For this reason, biochar once oxidized is also hydrophilic, thus making it desirable as a soil amendment due to its ability to attract and retain water. Biomass production via pyrolysis to obtain biofuels and biochar for carbon sequestration in the soil is a carbon-negative process, i.e. more C0 ₂ is removed from the atmosphere than released, thus enabling long-term sequestration.

Zeolites are microporous, aluminosilicate minerals commonly used as commercial absorbents and catalysts and some of the applications include odour control, contaminated site

remediation, fertiliser, water filtration and sewage treatment. Zeolites have a porous structure that can accommodate a wide variety of cations, such as Na ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ and others. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution. Zeolites occur naturally as a result of volcanic activity when a cloud of ash and small rocks falls into a brackish lake (giving rise to a Sodium zeolite) or into an alkaline lake (giving rise to a Calcium zeolite). Over eons of time these deposits are solidified into crystallized aluminosilicate minerals. Whilst zeolites can be manufactured synthetically, natural zeolite predominates the world’s annual production, about one hundred million tonnes annually. The majority of zeolite production comes from US and China, whilst there are a number of lesser producers. Natural zeolite has occurred in various environments and conditions, with different source materials and fluids that react with them at different temperatures and most importantly over different periods of time. This means that the properties of natural zeolites, such as hardness and specific density vary considerably depending on where it is from and which aluminosilicate minerals it comprises. There are over forty naturally occurring zeolite minerals of which mordenite, clinoptilolite, chabazite, erionite, phillipsite, laumontite, ferrierite and analcite are exploited commercially.

The hardness of zeolite mined in New South Wales, Australia is relatively hard and siliceous and has a high cation exchange capacity. For example, such zeolite from that region has a hardness greater than five (on the Mohs Hardness Scale) primarily due to it dating back at least three hundred million years. Whereas much of the zeolite commercially sourced from US and China and many other countries, has hardness of less than two, as it is less than thirty million years old. New Zealand zeolite from Lake Taupo also has hardness of less than 2, and it is less than fifteen million years old.

Biochar and zeolite each have their own advantages and are used independently in various applications, and in some applications such as in fertilisers where they are both used in small amounts. However, each of these materials suffer from certain disadvantages thus limiting the range of applications in which they are each used.

For example, most of the softer zeolites, particularly those having a Mohs Hardness of less than two, become clay-like and physically degrade into“mud” when exposed to water, thus making them unsuitable for water filtration and treatment. Zeolites also suffer a degradation in their functionality when subjected to oxidative conditions.

Pyrolysis of wood by itself yields a biochar which is soft, light (relative density 0.2-0.25), fluffy and which gets into everything, thus making handling of the material quite difficult. Also, when biochar is made from wood alone, there is a risk that it is inherently dangerous until fully cooled. A“hot spot” can cause spontaneous combustion in any bag or other container in which it is placed if not fully cooled.

They are known to be combined where zeolite makes up a small portion by mass. As disclosed in RU2655104 Cl(Obshchestvo S Ogranichennoj Otvetstvennostyu Kompaniya Novye Tekh) it is also known to take A-type synthetic zeolite in amount (wt%) 45-55 and combine it with kaolin 32-50, finely dispersed white carbon 1-5 and wood meal 4-8. The mixture moistened, mechanically granulated, dried, calcined, hydrothermally crystallized in an aluminate-alkaline solution, washed and then dried. It should be noted that the only organic material in this composition is the small amount of wood meal, whose primary purpose is to allow the inorganic components to bind when initially moistened and allow for granulation. Once the granulated composition is dried, calcined, crystallized and again dried, there is little left of what was the wood meal playing a role in the intended use of this composition. A-type synthetic zeolite has a cost of anywhere between ten times and a hundred times the cost of naturally sourced zeolite, so the cost of the granulated composition of this prior art, would be quite considerable, thus making it quite uneconomical for use in a variety of applications.

The present invention seeks to provide a composite material which overcomes at least one of the disadvantages associated with the prior art, by providing a composite material of biochar and zeolite.

SUMMARY OF INVENTION

According to a first aspect, the present invention consists in a method for preparing a composite material comprising:

(i) providing a biomass material and a zeolite:

(ii) mixing said biomass material and said zeolite together;

(iii) introducing said biomass material and said zeolite into a pyrolysis unit;

(iv) pyrolyzing said biomass material and zeolite so that the mixture becomes char and zeolite; and

(v) then allowing the resultant char and zeolite to be annealed to form said composite material; wherein said zeolite being provided at step (i) having a hardness of greater than four on the Mohs hardness scale and provided in a substantial amount so that the zeolite makes up no less than fifty percent by mass of said resultant composite material.

Preferably in one embodiment subsequent to step (iv) additional zeolite is added to said composite material.

Preferably in one embodiment said composite material undergoes an acid wash utilizing an acid selected from the group consisting of hydrochloric acid, acetic acid or phosphoric acid. Preferably in one embodiment said pyrolyzing temperature at step (iv) is in the range of 700- 740°C, and more particularly is about 720°C.

In a first specific embodiment said zeolite provided at step (i) has a size of 0.5-2.2mm and said biomass material is wood chip, and preferably said composite material is for use in water treatment.

In second specific embodiment said zeolite provided at step (i) has a size of up to 0.5mm and said biomass material is wood chip, and preferably said composite material is for use in treating blooms of algae in water.

In a third specific embodiment said zeolite provided at step (i) has a size of 3-7 mm and said biomass material is wood chip, and preferably said composite material is for use in treating gases and volatiles.

In a fourth specific embodiment said zeolite provided at step (i) has a size of up to 0.125 microns and said biomass material is wood chip, and preferably bentonite is mixed with said zeolite and said wood chip. Preferably the resultant composite material is for use in lick blocks for animals.

In an even further embodiment said pyrolyzing temperature at step (ii) is in the range of 400- 450°C. Preferably said zeolite provided at step (i) has a size of 2.2-2.5 mm and said biomass material is wood chip. Preferably either dried chicken manure, processed chicken litter or sewage sludge is added during the step (v). Preferably where processed chicken litter or sewage sludge is used, it is steam sterilised using heat generated by said pyrolysis unit.

Preferably the density of said composite material is in the range of 0.6-0.7, and more particularly about 0.65.

Preferably said composite material is in the range of fifty to seventy percent by mass of said composite material.

Preferably said zeolite being provided at step (i) having a hardness of greater than five on the Mohs hardness scale.

Preferably where said composite material has undergone an acid wash, said composite material is for use in water treatment where said zeolite binds cations by absorption and said char binds anions by adsorption. More preferably said cations are ammonium ions, and said anions are nitrate and/or phosphate ions.

In an even further embodiment said step (iv) and step (v) are carried out together, and the pyrolyzing temperature is preferably in the range of 600-740°C.

BEST MODE OF CARRYING OUT THE INVENTION

The present invention provides a method for preparing (or manufacturing) a composite material primarily comprising zeolite and biochar.

Firstly, a suitable zeolite and a suitable biomass material is required.

A suitable biomass material is wood. A suitable supply of wood is in the form of woodchips that have been stockpiled as by-product from other uses. In many instances and depending upon where and how the woodchips have been stockpiled, there is the advantage that the moisture therein has to some extent evaporated.

A suitable zeolite is one having hardness of greater than four, and more preferably greater than five on the Mohs Hardness Scale. One suitable zeolite is that mined in New South Wales (NSW), Australia and has a hardness greater than five. This zeolite herein referred to as“NSW zeolite” is dominantly clinoptilolite and mordenite, with small amounts of laumontite. This NSW zeolite with a hardness greater than five on the Mohs Hardness Scale is that which will be used.

In a first embodiment of the present invention the abovementioned woodchip and suitable zeolite (the NSW zeolite) are mixed together and then introduced into a pyrolysing unit to a temperature suitable to pyrolyze the wood into biochar and then having it annealed to the zeolite. A suitable pyrolysis temperature range is 700°C-740°C, but more preferably about 720°C.

The zeolite having a melting temperature of over 1000°C can easily withstand pyrolyzing temperatures of up to 900°C, and therefore does not undergo the thermochemical changes that occurs in the wood to biochar (char) transition.

Preferably the zeolite is provided in a substantial amount so that the zeolite makes up no less than 50% of the mass of the resultant composite material, and more preferably makes up fifty to seventy percent by mass of the composite material. Such resultant composite material is easily handled and managed. To do this, initially the wood chip to be mixed with the zeolite will be several times (usually about three to four times) the weight of zeolite. It should be understood the amount of moisture in the wood chip may vary considerably, and this must be taken in account when determining how much wood chip is to be mixed with the zeolite. It should be understood that without providing the wood chip in such a large quantity you cannot achieve a significant amount of biochar in the resultant composite material.

As the density of biochar produced by pyrolysis of wood alone would be about 0.2 to 0.25, and zeolite has a density approximate to 1, the abovementioned resultant composite material where zeolite makes up 50% (half) of its mass would have a density in the range of 0.6 to 0.7.

The resultant composite material also considerably reduces the risk of spontaneous

combustion that occurs from biochar produced by pyrolysis of wood alone.

What should be understood is the resultant composition is substantially a core of zeolite with the biochar predominantly in an outer layer, or crust along with zeolite and variably included moisture. It is important to note that the hardness of the zeolite, namely a hardness of greater than four on the Mohs hardness scale is essential to achieve this structure having a substantial core of zeolite inside a substantial outer layer of biochar.

As a result of the method of producing the abovementioned composite material, the porosity of the zeolite is reduced, and in some instances even filled, as a result of the biochar crust.

However, so long as an adequate availability of pores remain in the zeolite, the functionality of zeolite is retained. To further enhance the zeolite functionality of the composite material it is possible to add more zeolite to the composite material, after pyrolysis, which also assists in the cooling process.

Zeolites are negatively charged, so in water, they bind cations. To get the composite material to have the opposite charge and bind anions, the composite material may also be subjected to an acid wash with any one of 1M hydrochloric acid, 1M acetic acid or 1M phosphoric acid, with latter being the most preferred. This has the effect on the zeolite of replacing the normal sodium ion in the pores but puts surface positive charges on the biochar component of the composite material. Those sites which have no charge remain“uncharged” and will bind uncharged chemical moieties. An advantage of the abovementioned acid wash when carried out after pyrolysis is that assists in the cooling (quenching) process.

Examples will now be described with reference to various uses/applications. In all these examples the zeolite being used is“NSW zeolite” having a Mohs hardness greater than five. However, other zeolites having a Mohs hardness greater than four, could be used.

Example 1

Composite Material for use in Water Filtration

For potable water coming from a potable source dosed with Chlorine, particle filtration can be satisfactorily achieved with 0.5-2.2 mm zeolite to kill all infective biota.

Starting with 0.5 -2.2mm zeolite and wood chip are mixed together and then introduced into a pyrolysing unit at a temperature suitable to a pyrolyze the wood into biochar, as described earlier at about 720°C, and then annealed to the zeolite, with the option of adding more zeolite after pyrolysing. The zeolite is provided in a substantial amount so that the zeolite makes up fifty to seventy percent by mass of the resultant composite material. This resultant composite material retains the“hard blocky” form of the zeolite used in this process.

Then subjecting the same to an acid wash as described earlier.

The stable resultant composite material is easily handled and managed, and also suitable for use in filtration and treatment of waste, storm and industrial waters.

Zeolites bind cations most frequently ammonium ions by absorption in the pores of their structure. Acid modified char binds anions including but not limited to nitrate and phosphate on their surface by adsorption. Collectively this amounts to binding total nitrogen (TN) and total phosphorus as phosphate (TP). TN and TP are used by regulatory authorities to define the maximum residual levels of these nutrients in waste, storm and other waters allowable to be released into the environment. Because of this ability by zeolite to bind cations and the acid modified char to bind anions, the stable composite material formed in this example is ideally suited for the abovementioned uses of filtration of waste, storm and industrial waters. Example 2

Pond - Water treatment

Starting with 0-0.5mm zeolite and wood chip and carrying out the various steps as in abovementioned Example 1.

The resultant composite material is suited to treat blooms of algae, Cyanophyte (blue-green bacteria), and water ferns by gentle removal of the inorganic nutrients (TN and TP as in Example 1) that bind to the composite material. The composite material will also bind any toxin that emanates from the treatment as a result of stressing the Cyanophytes, which is highly advantageous.

Example 3

Gases and Volatiles treatment

Starting with 3 -7mm zeolite or even larger sized zeolite particles, the zeolite and woodchips are mixed together and then introduced in a pyrolysing unit to a temperature as described earlier at about 720°C suitable to a pyrolyze the woodchip into biochar and then annealed to the zeolite, with the option of adding more zeolite after pyrolysing. The zeolite is provided in a substantial amount so that the zeolite makes up fifty to seventy percent by mass of the composite material.

The resultant composite material is used mixed with a chemical oxidant or reductant to attract water in an air stream and treat malodorous volatiles including hydrogen sulfide (EES) and ammonia (NEE) in anaerobic conditions as in sewage treatment plants or nitrogen dioxide (NO2), carbon monoxide (CO) which will bind to the primarily outer layer of char of the resultant composite material, and sulfur dioxide (SO2) in air, such as in exhaust stacks over motorway tunnels and the like.

Example 4

Lick blocks for animals (including sheep, goats, cattle and horses)

Starting with 0-125 micron zeolite, the zeolite, wood chip and bentonite are mixed together and then introduced into a pyrolysing unit to a temperature as described earlier at about 720°C suitable to a pyrolyze the woodchip into biochar and then annealed to the zeolite as described earlier. The zeolite is provided in a substantial amount so that the zeolite makes up fifty to seventy percent by mass of the composite material. The bentonite is provide in an amount such that it makes up twenty five to thirty percent of the composite material.

Then subjecting same to an acid wash as described earlier, so that surface positive charges are placed on the biochar component of the composite material.

The resultant composite material assists in the homing of microbes and the binding of toxins of plant, fungal and bacterial origin due to the increased surface area provided by the bentonite in the resultant composite material. It also affects the binding and elimination of toxins and homeostasis between the GI tract organs, especially the liver.

Other inputs into the final block that comprise this composite material include but are not limited to salt and molasses as well as metabolic intermediates such as Vitamin C,

monosodium glutamate (MSG), glycerol, triglycerides, enzymes as well as probiotic and other bacteria, to assist in providing added nutritional supplement to the animals.

So far we have demonstrated efficacy in the treatment of poisoning of cattle by plants, including several native peas and wattles, two species of rice flowers (Pimelia spp) and Lantana. Studies by others have shown that the rumen microbes can break down these toxins over time.

The added probiotic bacteria to the lick block assists in the prevention and treatment of plant poisoning not only to cattle but also sheep.

We have also demonstrated efficacy in reducing lead poisoning in cattle utilising the lick block of this example. Cattle are attracted to the taste of lead , whether that be in processed form such as in lead batteries in a farm environment, or in pasture areas in proximity to lead deposits. The lick blocks of the present embodiment containing the resultant composite material and zeolite is effective in stripping out lead as measured in blood levels of the cattle.

In addition to the examples above it should be understood that other uses of the resultant composite material are as supplemental feed additives where probiotic bacteria added to the composite material are effective in the treatment of scours in most young animals and intractable diarrhoea in dogs. The composite material can also be used in the treatment of other metabolic syndromes including but not limited to milk fever in cows and big head and laminitis in horses. It is most likely that the composite material of the present embodiments will find a place in supplemental feeds for meat producing animals and birds, to increase their growth rates.

Whilst the abovementioned embodiments and examples utilise a pyrolysis temperature range of 700°C-740°C, it is possible to prepare a composite material having different properties by utilising a lower temperature range. The following examples 5 and 6 utilises a lower range pyrolysis temperature.

Example 5

Manure filled composite material

Starting with 2.2-5 mm zeolite and woodchip are mixed and then introduced into a pyrolysing unit to a temperature range of 400-450°C suitable to pyrolyze the woodchip into biochar and then annealed to the zeolite, with the addition of“steam sterilised chicken manure” during annealing and optionally adding more zeolite to produce a composite material. The zeolite is provided in a substantial amount so that the zeolite makes up no less than fifty percent by mass of the composite material.

Because of the size and nature of the materials and the lower pyrolysis temperature the thermochemistry differs to that of pyrolysis of the earlier mentioned embodiments (at higher temperatures of about 720°C). The lower temperature pyrolysis combined with the mixing of dried chicken manure results in a composite material with greater air-filled porosity because of the size of the zeolite.

To maximise the efficiency of the biochar component, it is possible to add some inorganic chemicals such as for example but not limited to ferrous sulfate and manganous sulfate, that act as activators.

The resultant composite material has application in soil ameliorants and/or potting mix ingredients.

In an alternative embodiment to that of Example 5, the pyrolysis of the zeolite and woodchip is carried out in the same way at the lower temperature range of 400-450°C, however the chicken manure instead of being steam sterilised, undergoes thermophilic composting at temperatures in the range of 45-75°C before being mixed with the composite material.

It should be understood, that in another alternative embodiment, the chicken manure may be treated by other means before being mixed with the composite material. Example 6

Carbon based fertiliser

2.2-5 mm zeolite and woodchip are mixed and then introduced in a pyrolyzing unit at a temperature in the range 400-450°C to pyrolyze the wood into biochar and then annealed to the zeolite.

The heat generated in the pyrolysis process is used to steam sterilise“sewage sludge” and/or “fine processed chicken litter”, which would then be admixed into the composite material as it is being annealed, to make a high carbon and nitrogen fertiliser. The zeolite is provided in a substantial amount so that the zeolite makes up no less than fifty percent by mass of the composite material.

The lower temperature pyrolysis combined with the mixing of sewage sludge” and/or“fine processed chicken litter” results in a composite material with greater air-filled porosity because of the size of the zeolite.

Potassium could be added to this composite material, with one suitable source of potassium is “cotton trash”.

It should be understood that in other embodiments at temperatures in the range of 600-740°C, the woodchip (biomass material) and zeolite can be pyrolized, so that the mixture becomes char and zeolite and in the same step be annealed to form said composite material.

Whilst the zeolite being used in the abovementioned examples is“NSW zeolite” having a Mohs hardness greater than 5, it should be understood, that other zeolite having a Mohs hardness of greater than 4 could be used.