Method for extracting soluble Si from an amorphous SiO.SUB.2 .bearing material

Abstract

The present invention relates to bioavailable (which may also be referred to as plant available) silicon, such as in the form of a concentrate or solid, and processes for producing and using bioavailable silicon.

Claims

1. A method for extracting soluble Si compounds from an inorganic amorphous silica bearing material, the method including: leaching the inorganic amorphous silica bearing material with an alkaline solution in a reaction mixture to convert at least a portion of amorphous silica in the inorganic amorphous silica bearing material to a soluble silicic species and form a leachate including the soluble silicic species and a solid residue; and separating the leachate from the solid residue to form an aqueous leachate solution, wherein an amount of the alkaline solution of a sufficient pH is used so that, after the step of separating the leachate from the solid residue, the leachate has a pH of 11 or greater; wherein the step of leaching the inorganic amorphous silica bearing material with the alkaline solution is conducted at a temperature of from ambient to 95° C.; and wherein the step of leaching the inorganic amorphous silica bearing material with the alkaline solution is conducted in the absence of a humic acid-containing raw material.

2. The method of claim 1, wherein the step of leaching the inorganic amorphous silica bearing material with the alkaline solution includes initially forming a reaction mixture of the inorganic amorphous silica bearing material and the alkaline solution.

3. The method of claim 2, wherein the method further includes heating the reaction mixture to a temperature greater than ambient and up to 95° C. under ambient pressure.

4. The method of claim 2, wherein the inorganic amorphous silica bearing material is present in the reaction mixture at an amount of from about 5 wt % to about 85 wt %.

5. The method of claim 1, wherein the alkaline solution is a potassium hydroxide solution.

6. The method of claim 5, wherein KOH is present in an amount of from 20 g/L up to 120 g/L.

7. The method of claim 1, wherein the step of leaching the inorganic amorphous silica bearing material with potassium hydroxide is conducted for a time of at least 0.5 hours and up to 96 hours.

8. The method of claim 7, wherein the time is up to 8 hours.

9. The method of claim 1, wherein the step of leaching the inorganic amorphous silica bearing material with the alkaline solution is conducted at a temperature of from about 50° C. to about 95° C.

10. The method of claim 1, wherein the reaction mixture includes an amount of the alkali solution of the sufficient pH to provide the reaction mixture with an initial pH of 10.8 or greater.

11. The method of claim 1, wherein the step of leaching the inorganic amorphous silica bearing material with the alkaline solution is conducted at ambient pressure.

12. The method of claim 1, wherein the inorganic amorphous silica bearing material is diatomaceous earth.

13. The method of claim 1, wherein the soluble silicic species is in the leachate at a concentration of from 10 g-Si/L to 100 g-Si/L.

14. The method of claim 1, wherein the solid residue includes residual potassium silicates.

15. The method of claim 1, wherein the method further includes subjecting the aqueous leachate solution to evaporation to further concentrate the soluble silicic species.

16. The method of claim 1, wherein the method further includes diluting the aqueous leachate solution to a pH suitable for application to plants.

17. A method for preparing a solid residue including reacted silica from an inorganic amorphous silica bearing material, the method including: treating the inorganic amorphous silica bearing material with an alkaline solution in a reaction mixture to convert at least a portion of amorphous silica in the inorganic amorphous silica bearing material to a reacted silica and form a leachate and a solid residue including the reacted silica; and separating the leachate from the solid residue to form an aqueous leachate solution, wherein an amount of the alkaline solution of a sufficient pH is used so that, after the step of separating the leachate from the solid residue, the leachate has a pH of 11 or greater; wherein the step of treating the inorganic amorphous silica bearing material with the alkaline solution is conducted at a temperature of from ambient to 95° C.; and wherein the step of treating the inorganic amorphous silica bearing material with the alkaline solution is conducted in the absence of a humic acid-containing raw material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Effect of temperature on the pH and concentration of silicon within solution over a six-hour agitation period.

(2) FIG. 2: Effect of temperature on the reaction rate and extent of leaching as per silicon concentration within solution (adjusted for evaporation).

(3) FIG. 3: Effect of initial diatomite concentration on silicon extraction into solution as a function of reaction time.

(4) FIG. 4: Effect of initial diatomite concentration on the pH of solution as a function of reaction time.

(5) FIG. 5: Effect of initial potassium hydroxide concentration on silicon extraction and the pH of solution as a function of reaction time.

(6) FIG. 6: Comparison of dilution rates on solution pH for silicon solutions prepared with K.sub.2CO.sub.3 against KOH.

(7) FIG. 7: Silicon and potassium concentration within solution extracted from leach residue with increasing wash stages.

(8) FIG. 8: Effect of claimed concentrated silicon solution on Queensland sweetcorn at specified dilution and application rates in comparison to standard fertiliser practices

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) The present invention generally relates to methods for forming a soluble silicon compound (in the form of silicic acid) concentrate, particularly for use as a fertiliser. Typically, the concentrate includes the soluble silicon compound in an amount of about 20 wt % with a solution pH in the range of 11-12. This concentrate can be diluted to form a silicon containing fertiliser with a pH appropriate for application to plants.

(10) Table 1 provides concentrate product specifications according to one embodiment.

(11) TABLE-US-00001 TABLE 1 Concentrate product specifications according to one embodiment. DESCRIPTION UNITS VALUES Silicon (Si) w/v 6.0 As silicic acid (H.sub.4SiO.sub.4) w/v 20.5 Potassium (K) w/v 5.0 Solution pH — 11-12 SG — 1.10-1.20

EXAMPLE 1

(12) Comparison of Silicon Concentrations within Solution at Relevant Solution pH Levels and their Respective Dilution Rates

(13) Solution samples were cyclically diluted in tap water, which was measured at pH 7.3 on the day of the tests. The cyclically diluted solutions were then sampled and diluted with sodium hydroxide (NaOH) solution for subsequent silicon concentration measured by ICP. The pH of each diluted solution was measured after completing the set of dilutions, measuring from lowest to highest to avoid cross contamination of alkaline solution into the diluted solutions.

(14) Table 2 below provides solution pH and silicon concentration data interpolated between common dilution ratios compared with the alternative potassium silicate solution. This table shows that the alternative solution, while starting at a higher silicon concentration, ends up at a significantly lower silicon concentration after being diluted to a pH suitable for application to crops when compared with the solution of Table 1.

(15) TABLE-US-00002 TABLE 2 Comparison of current claimed solution as per Table 1 and commercial potassium silicates with increasing dilution rates SOLUTION SILICON CONCENTRATION pH (mg/L) Current Commercial Current Commercial DILUTION Claimed Potassium Claimed Potassium RATE (L/L) Solution Silicate Solution Silicate — 11.8 12.4 60,000 170,000 10 10.8 11.4 6,000 17,000 100 9.8 10.4 600 1,700 300 9.3 9.9 200 567 500 9.1 9.7 120 340 1,000 8.8 9.4 60 170 3,500 8.3 8.9 17 49 5,000 8.1 8.7 12 34

(16) It is preferred to produce a concentrated silicon solution with a final solution pH and silicon concentration within a range that allows for dilution to a pH suitable for application to crops, whilst maintaining a relatively high concentration of silicon within solution.

EXAMPLE 2

(17) Effect of Temperature on Reaction Rate and Extent

(18) Effect of temperature on reaction rate and extent was evaluated in this example by reacting two samples of diatomite with K.sub.2CO.sub.3 in parallel experiments at room temperature and 50° C. Overhead impellers were inserted into two 1 L baffled glass reactors, and one reactor placed onto a hot plate.

(19) 520 g of DI water and 480 g of K.sub.2CO.sub.3 was added to each reactor, and the solutions agitated with the overhead impellers at 1,000 revolutions-per-minute (RPM) until no solid alkali was observable. pH and temperature probes were submerged within solution, and the hot plate was adjusted proportionally until the slurry temperature stabilised. 200 g of diatomite was added to each reactor and time was recorded with a stopwatch; with sampling of slurry conducted at intervals of 1, 2, 4, and 6 hours with a syringe filter, and pH and temperature of the slurry was recorded at each sampling interval.

(20) FIG. 1 illustrates the effect of temperature on the kinetics of silicon extraction and pH for experiments conducted in parallel at room temperature and 50° C. Extraction rate within solution is significantly increased at 50° C. compared to at room temperature; approximately 7000 mg.sub.Si/L versus 365 mg.sub.Si/L after six hours of agitation, respectively.

(21) The pH of solution exhibited similar trends for both trials; however, at 50° C. the pH of solution reached significantly lower value as compared with the room temperature pH of solution. The relationship between pH and hydroxide concentration is provided in Eqn. 1, and the generation of silicate anions in Eqn. 2.
pH-14=−log H.sup.+−14=log OH.sup.−  Eqn. 1
H.sub.4SiO.sub.4+nOH.sup.−.Math.H.sub.4-nSiO.sub.4.sup.n−+nH.sub.2O  Eqn. 2

(22) Further kinetic experiments relevant to this example investigated effects of temperature on reaction rate and extent over a wider range of temperatures with a KOH lixiviant. Kinetic tests were conducted at 50, 70, 80 and 90° C.

(23) Due to the incremental upscaling of feed mass and equipment limitations, differing equipment modalities were chosen for various tests. 50° C. test utilised a horizontal shaking water bath, with a feed mass of 500 g and three replicates. 70° C. and 80° C. utilised a baffled 20 L electrically heated benchtop vessel, powered by a low shear rotary impeller. Feed mass was 10,000 g. As evaporative losses were a concern at 90° C., an electrically heated pressurised vessel horizontally rotating digestion unit was utilised. Feed mass was 40 g with six replicates.

(24) Each experiment was conducted with the same feed composition as detailed in Table 3. Reaction time varied for each sample, however sampling was conducted on a regular basis to allow for comparison of reaction kinetics.

(25) TABLE-US-00003 TABLE 3 Details of experiments investigating the effects of temperature on reaction rate and extent TOTAL TEMPERATURE DIATOMITE KOH WATER MASS TRIAL (° C.) (g) (g) (g) (g) 1 50 167 25 309 501 2 70 3,330 500 6,170 10,000 3 80 3,330 500 6,170 10,000 4 90 13.3 2.0 24.7 40

(26) FIG. 2 compares the reaction rates of silicon dissolution at temperatures 50° C., 70° C., 80° C., and 90° C. under constant experimental conditions. Characteristic of all tests is an initial linear response followed by a parabolic rate as the concentration of hydroxide declines, and a silicon solubility limit is indicated.

(27) Table 4 provides a useful comparison of the results, utilising regression analysis to determine time elapsed at a silicon concentration that is 90% of the final recorded value. The declining rate yield with temperature indicates that the accelerated kinetics are less significant once solubility equilibrium is approached, with a substantial rate increase from 50° C. to 70° C., a moderate improvement at 80° C., and a minor improvement at 90° C.

(28) TABLE-US-00004 TABLE 4 Comparison of rate of reaction with varying temperature at 90% of final extraction VALUES AT 90% FINAL LEACHING TEMPERATURE (° C.) EXTRACTION 50 70 80 90 Silicon (g/L) 41.3 59.5 63.2 60.1 Leaching time (hrs) 35.5 3.5 2.1 1.7

(29) Higher temperatures, such as from 70° C. to 90° C., are preferred for this process, at a range where reaction kinetics and extent are optimised in conjunction with the practical and economic aspects of maintaining high temperatures within solution.

EXAMPLE 3

(30) Effect of Initial Diatomite Concentration in Leaching

(31) Effect of initial diatomite concentration in leaching was evaluated in this example by reacting four samples of diatomite with K.sub.2CO.sub.3 in parallel experiments in triplicate at room temperature. Reagents and DI water were added to 250 mL HDPE wide-mouth containers as per Table 5. Containers were placed in a bottle roller set at 40 RPM. Samples were maintained at 25° C. via a water bath situated within the bottle roller.

(32) The samples were left overnight to ensure dissolution of the reagents within the containers. Diatomite was added to the respective containers, which were then placed back into the bottle roller to commence agitation; time was recorded and sampling was conducted at intervals of 4, 8, 24, 48, 96, 168, and 336 hours' total agitation time over a two-week period.

(33) TABLE-US-00005 TABLE 5 Details of experiments investigating the effect of initial diatomite concentration in leaching TEMPER- TOTAL ATURE DIATOMITE K.sub.2CO.sub.3 WATER MASS TRIAL (° C.) (g) (g) (g) (g) 1 25 33.3 33.3 133.3 200 2 25 20.0 33.3 146.7 200 3 25 10.0 33.3 156.7 200 4 25 2.0 33.3 164.6 200 *Note: The ratios of K.sub.2CO.sub.3 to DE used in these experiments were about 1000 g.sub.KOH/Kg-DE, 1665 g.sub.KOH/Kg-DE, 3330 g.sub.KOH/Kg-DE, and 16650 g.sub.KOHH/Kg-DE.

(34) FIG. 3 outlines the effects of the initial amount of diatomite addition on the silicon concentration in solution, whilst maintaining KOH addition and temperature between experiments. Initial diatomite concentrations within solution were: 16.6%, 10.0%, 5.0%, and 1.0%. Trend lines for initial diatomite concentrations of 16.6%, 10.0%, and 5.0% exhibit a similar rate of reaction. The solution with an initial diatomite concentration of 1.0% did not reach similar silicon concentrations relative to the other samples, due to depletion of available silicon within the diatomite.

(35) FIG. 4 outlines the effect of initial diatomite concentration on the pH of solution. A significant decrease in pH is observed initially, which increases with diatomite content. Solution pH stabilises as the reaction extent reaches equilibrium under these process conditions. The relatively high solution pH and low silicon concentrations observed with the 1.0% diatomite trial indicate that the reaction was not limited by process conditions, but rather a lack of available silicon within the material at these rates.

(36) Experiments were conducted in a stainless steel, baffled 20 L electrically heated benchtop vessel, powered by a low shear rotary impeller. Slurry temperature was maintained at 80° C., reaction time at two-hours, and total feed mass of diatomite, KOH, and water was maintained at 10,000 g for each experiment as per Table 6.

(37) Table 6 outlines the effect of varying diatomite concentration within solution. Increasing solution recovery via filtration is linked to decreasing diatomite concentration, whilst increased silicon concentration within solution is linked to increasing diatomite concentration.

(38) TABLE-US-00006 TABLE 6 Comparison of key operational parameters as a function of diatomite concentration within initial solution INITIAL DIATOMITE CONCENTRATION 33.0% 25.0% 16.7% PARAMETER UNITS DE DE DE Initial KOH wt % 5.0 8.0 5.0 Initial diatomite wt % 33.0 25.0 16.7 Solution recovered wt % 46 59 71 Solution pH — 12.1 12.9 13.6 Solution concentration g.sub.Si/L 60.9 54.6 36.3 * Note: The ratios of KOH to DE used in these experiments were about 100 g.sub.KOH/Kg-DE, 240 g.sub.KOH/Kg-DE, and 250 g.sub.KOH/Kg-DE.

(39) It is preferred to maintain initial diatomite concentration at a range where reaction extent is not limited by available silicon within initial material and final solution pH is maintained at levels practical for dilution applications, whilst still maintaining practical and economical recovery of solution via filtration of reacted slurry.

EXAMPLE 4

(40) Effect of Initial Potassium Hydroxide Concentration in Leaching

(41) Effect of initial potassium hydroxide concentration in was evaluated in this example by reacting three samples of diatomite with KOH at 80° C. for two-hours. Overhead impellers were inserted into the 1 L baffled glass reactors, which was subsequently placed onto a hot plate.

(42) DI water and KOH was added to each reactor as per Table 7 and the solutions agitated with the overhead impellers at 1,000 RPM until no solid alkali was observable. pH and temperature probes were submerged within solution, and the hot plate was adjusted proportionally until the slurry temperature stabilised. 330 g of diatomite was added to each reactor and time was recorded with a stopwatch; with sampling of slurry conducted at intervals of 15, 30, 60, 90, and 120 minutes with a syringe filter, and pH and temperature of the slurry was recorded at each sampling interval.

(43) FIG. 5 outlines the effects of the initial KOH addition rates on the silicon concentration and pH in solution; whilst maintaining diatomite addition at 30 wt % and temperature at 80° C. between experiments. Initial KOH concentrations within solution were: 81 g.sub.KOH/L, 175 g.sub.KOH/L, and 250 g.sub.KOH/L (which amounts are equivalent to about 160 g.sub.KOH/kg-DE, 345 g.sub.KOH/kg-DE, and 490 g.sub.KOH/kg-DE respectively). Extraction rates and final silicon concentration showed significant increases above 80 g.sub.KOH/L, which settled at approximately 60 g.sub.Si/L after 60 minutes of reaction time. Initial addition rates of 175 g.sub.KOH/L and 250 g.sub.KOH/L demonstrated an increased silicon extraction rate, however this levelled out after 60 to 120 minutes of reaction time to approximately 90,000 mg.sub.Si/L. This may indicate that at approximately 90,000 mg.sub.Si/L there is a silicon solubility limit under these process conditions; hence limiting further dissolution of silica.

(44) Initial KOH concentration increases the initial solution pH, due to the number of free hydroxides (OH.sup.−) formed upon dissolution. Eqn. 3 outlines the driving reaction mechanism for the dissociation of silica into an available ionic silicate speciation. This reaction will proceed until equilibrium under process conditions, until free hydroxides are depleted, or until available silica is depleted.
SiO.sub.2+4OH.sup.−.Math.SiO.sub.4.sup.4−+2H.sub.2O  Eqn. 3

(45) Whilst the initial KOH addition rates of 175 g.sub.KOH/L, and 250 g.sub.KOH/L both reached a similar final silicon concentration, free hydroxides were depleted at similar rates until this limit was reached; final solution pH's were approximately 12 and 13, respectively. It is preferred to maintain final solution pH at a minimum if similar concentrations of silicon can be achieved; optimising initial KOH addition rates where excess is not added and diminishing returns on silicon extraction are observed.

(46) Table 7 summarises the effects of the initial KOH addition rates on product characteristics. Increasing the initial KOH addition rates significantly increases the solution recovery rate via filtration, however this rate decreases with increasing addition.

(47) Relative silicon concentration within solution at pH 9, assuming linear dilution, is seen to decrease significantly due to the logarithmic nature of pH requiring an order of magnitude increase in silicon concentration to match a similar linear increase in pH.

(48) TABLE-US-00007 TABLE 7 Comparison of key operational parameters as a function of potassium hydroxide concentration within initial solution PARAMETER UNITS 81 g.sub.KOH/L 175 g.sub.KOH/L 250 g.sub.KOH/L Initial mass g 1,000 1,000 1,000 Initial KOH wt % 5.0 10.0 13.0 Initial KOH g.sub.KOH/L 80.6 175.4 250.0 Initial diatomite wt % 33.0 33.0 33.0 Solution recovered wt % 46 57 59 Solution pH — 12.1 12.9 13.8 Solution concen- g.sub.Si/L 60.9 91.1 89.8 tration Concentration after mg.sub.Si/L 48 11 <1 dilution to pH 9

(49) It is preferred to maintain initial KOH addition at a range where silicon extraction rate and concentration is maximised relative to the final solution pH and required dilution ratio, whilst ensuring that recovery of filtrate is optimised against practical and economic aspects.

EXAMPLE 5

(50) Comparison of Dilution of Silicon Solution Produced Using Potassium Carbonate Versus Potassium Hydroxide

(51) For the concentrated soluble silicon solution to be applicable to industry it should be within physiological pH ranges, requiring dilution typically with water. Due to pH being measured on the logarithmic scale, there is a trade-off between concentrated solution pH and the amount soluble silicon within solution; it may be preferable to select a solution with a lower soluble silicon content and a low pH than one with a high soluble silicon content and a high pH.

(52) Dilution of a sample reacted with a 40.0 wt % K.sub.2CO.sub.3 lixiviant was conducted via cyclic diluted in tap water, which was measured at pH 7.3 on the day of the tests. The cyclically diluted solutions were then sampled and diluted with sodium hydroxide (NaOH) solution for subsequent silicon concentration measured by ICP. The pH of each diluted solution was measured after completing the set of dilutions, measuring from lowest to highest to avoid cross contamination of alkaline solution into the diluted solutions.

(53) Table 8 outlines the decrease in pH and concentration with dilution, reaching a pH of 9.97 and concentration of 0.6 ppm after a dilution factor of 10,000.

(54) TABLE-US-00008 TABLE 8 Effects of dilution on a sample reacted with K.sub.2CO.sub.3 lixiviant with DI water on solution pH and silicon concentration DILUTION SOLUTION SILICON CONCENTRATION RATE pH (mg/L) 1 12.39 5,400.00 10 11.31 540.30 100 11.29 53.75 1,000 10.77 5.55 10,000 9.97 0.58

(55) FIG. 6 displays the relationship between the log molar concentrations of silicon in solution with pH. The linear trend indicates that silicon remains within solution at all stages of dilution. However, pH values for the 10× dilution and 100× dilutions were 11.31 and 11.29, respectively, this small pH drop indicates other factors influencing the required dilution. The sample contained high levels of K.sub.2CO.sub.3, which dissociates in solution to form bicarbonate ions. These bicarbonate ions then act as buffers in the presence of hydrogen ions as the pH is decreased; significantly decreasing the pH drop independent of the concentration decrease.

(56) It is preferred that potassium hydroxide is used as the lixiviant for the production of the concentrated silicon solution as opposed to carbonate reagents. This is because the concentrated silicon solution typically requires dilution to reach an appropriate pH prior to application. Carbonate reagents increase the buffering capacity of the solution which in turn means that further dilution is required to reach the appropriate pH. Additionally, potassium is generally a useful mineral for plants.

EXAMPLE 6

(57) Washing to Recover Extra Silica

(58) Effect of washing to recover extra silica was evaluated in this example with leach residue that was produced by reacting diatomite with KOH at 80° C. for three-hours in a 3.5 L baffled stainless steel reactor on a hot plate, with an overhead impeller inserted into the reactor. Total initial mass of the leach was 3,000 g, with 1,000 g diatomite and 2,000 g of 80 g.sub.KOH/L solution. Upon completion of the leach, the slurry was filtered through a 20 L pressure filter. Once filtrate had been recovered, the mass was measured and the proportional amount of wash-water was added to the filter, and filtration repeated.

(59) Filtration of leached slurry is applied to remove the concentrated silicon solution from the reacted diatomite. Leach solution may remain with the solid fraction upon filtering due to filtration inefficiencies, or potassium, silicate, and hydroxide ions adsorbing or precipitating out of solution as moisture is removed. Washing the dewatered solids with water or alkali solution may increase the solubility of these ions, recovering them into the wash solution as potential product.

(60) FIG. 7 displays the silicon and potassium concentration within solution extracted from leach residue with increasing wash stages at 1:1 wash water to dried solid filtrate ratio. Initial silicon concentration of filtered product solution was 44 g.sub.Si/L. Filtered residue was then subject to application of the same mass of liquid removed, whilst remaining within the filter vessel. Filtrate from this wash stage had a total silicon concentration of 42 g.sub.Si/L, a decrease of approximately 4%. Further wash stages recovered additional dissolved silicon albeit at lower solution concentrations.

(61) It is preferred to incorporate a wash stage to the filtered solids to increase silicon recovery and solution production, whilst maintaining product specifications.

EXAMPLE 7

(62) Effect of Evaporation on Concentrated Silicon Solution

(63) An additional advantageous approach to achieve production of a concentrated silicon containing fertiliser is to include a stage of solution evaporation. Evaporation of the silicon solution may be conducted to further increase the concentration of this solution via removal of excess water. The evaporation process may be carried out using natural, thermal, or vacuum evaporation. During an evaporation process a portion of the water contained within the solution will be removed while the dissolved potassium and silicon ions will remain in the solution, up to the point where they reach their solubility. The main advantage of increasing the silicon concentration in solution by evaporation is that it decreases the amount of solution to be handled and transported to the required location for application, hence providing economic and practical advantages.

(64) The evaporation step is effectively the opposite of the dilution step carried out just prior to applying the solution to plants. The dilution step is required so that the solution is applied to the plants at a suitable pH. Because the evaporation step has the opposite effect to the dilution step, the silicon concentration and pH will still have the same relationship and hence the solution applied to the plants will still have the same pH and silicon characteristics such as those described in example 1. An estimate of the effect of varying extents of water evaporation on the solution volume and characteristics is presented in Table 9.

(65) TABLE-US-00009 TABLE 9 Theoretical effect of water evaporation on the concentrated silicon containing solution EVAPORATION EVAPORATION PARAM- INITIAL OF 20% OF 50% ETER UNITS VOLUME VOLUME VOLUME Potassium g/L 50.0 62.5 100.0 Silicon g/L 50.0 62.5 100.0 pH — 11.5 11.6 11.8

EXAMPLE 8

(66) Effect of Claimed Concentrated Silicon Solution at Specified Application Rates Versus the Standard Fertiliser Practices on Crop Growth and Development

(67) The claimed concentrated silicon solution was trialled at specified foliar application rates with the standard fertilising practices (SFP) and against the SFP. Three replicated, small plot field trials were conducted in Australia on a specified variety of sweetcorn and soil. Silicon solution was applied at rates of 9 L/ha and 15 L/ha with the SFP application, and these were conducted in parallel against the control application of the SFP.

(68) FIG. 8 displays the increase in number and yield of marketable cobs per 100 plants, and also the increase in brix relative to the SFP with the applications of 9 L/ha and 15 L/ha in conjunction with the SFP.

(69) A separate field trial was conducted in Australia to evaluate the effect of the claimed concentrated silicon solution at specified foliar application rates with the SFP and against the SFP. Two replicated field trials were conducted on a specified variety of chickpea and soil. Silicon solution was applied at a rate of 4 L/ha with the SFP application, and this was conducted in parallel against the control application of the SFP.

(70) Table 10 displays the increase in yield of chickpea with the application of the SFP plus 4 L/ha of the claimed concentrated silicon solution relative to the SFP and no addition of a silicon concentrate.

(71) TABLE-US-00010 TABLE 10 Effect of claimed concentrated silicon solution at a specified application rate of 4 L/ha with the SFP versus the SFP on crop growth and development PARAMETER UNITS SFP SFP + 4 L/ha Yield (tonnage) t/ha 0.66 0.72 Yield (percentage) % 100 110

EXAMPLE 9

(72) Preparation of Solid Residue Including Silicic Species.

(73) There are two primary accepted methods for measuring plant available silicon or plant available silicon.

(74) The method used in the USA for measuring plant available or soluble silicon of solid fertilisers includes a 5-Day test with Na.sub.2CO.sub.3—NH.sub.4NO.sub.3 test. This test does not convert insoluble amorphous silica to a soluble form, but rather promotes the dissolution of already soluble silicic species for measurement.

(75) Another accepted method for measuring plant available silicon is via extraction with a 0.01M Calcium Chloride solution. 0.01M CaCl.sub.2 is known to extract readily available soluble silicic species and is therefore a good measure of the immediately available silicon for plant uptake. As with the testing method used in the USA, this method does not convert insoluble amorphous silica to a soluble form.

(76) In the present case, amorphous silica bearing material is treated with an alkali solution. Table 9 below provides a comparative summary of the soluble silicon species in Wollastonite in comparison with soluble silicon species in calcium silicate slag and the solid residue prepared from solubilising an amorphous silica containing material with an alkali. It will be appreciated that higher concentrations of soluble silicon are attainable depending on the processing conditions.

(77) TABLE-US-00011 TABLE 9 Plant available silicon as measured by the SLV 5-Day Na.sub.2CO.sub.3—NH.sub.4NO.sub.3 method and the 0.01M CaCl.sub.2 method ppm Soluble Silicon measured by SLV 5-Day 0.01M Sample Na2CO3—NH4NO3 CaCl2 method Wollastonite 31,373 2,079 (Vansil W30) Calcium Silicate Slag 3,129 274 Solid Residue 38,944 10,993

(78) As can be seen from Table 9, the solid residue has a significantly higher level of silicic species than calcium silicate slags, that are commonly used as fertilisers. Therefore, the amorphous silica is a useful starting material in preparing a solid residue with a high concentration of soluble or solubilisable silicon.

EXAMPLE 10

(79) Production of Solid and Liquid Fertiliser Including Silicic Species from Rice Hull Ash.

(80) A portion of rice hull ash (RHA) having a chemical analysis of: SiO.sub.2 (94-99%), Carbon (1-5.5%), Moisture (<1%) is fed into a reactor containing 1.5M KOH solution to form a slurry having a solids content of about 30 wt % solids and a pH of about 13.5 at ambient temperature and atmospheric pressure. The slurry is heated up to about 80° C. and agitated to maintained dispersion of the RHA in the slurry. The leaching reaction is maintained for 2 to 6 hours by which time 50% of silica contained in the RHA has been dissolved into the leachate. The slurry is then filtered to separate the solids (mainly including organic carbon, metals, soluble silicic species and unreacted silica) from the leachate. The solids includes entrained leachate and has a moisture content of 40% w/w solids.

EXAMPLE 11

(81) Production of Solid and Liquid Fertiliser Including Silicic Species from Glass

(82) A portion of crushed glass having a chemical analysis of: SiO.sub.2 (>99%), Moisture (<1%) is fed into a reactor containing 2M KOH solution to form a slurry having a solids content of about 20 wt % solids and a pH of about 14 at ambient temperature and atmospheric pressure. The slurry is heated up to about 90° C. and agitated to maintain dispersion of the crushed glass in the slurry. The leaching reaction is maintained for 2 to 6 hours by which time 20% of silica contained in the glass has been dissolved into the leachate. The slurry is then filtered through a filter to separate the solids (mainly including soluble silicic species and unreacted silica) from the leachate. The solids includes entrained leachate and has a moisture content of 30% w/w solids.

(83) It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.