Method for purifying high-purity quartz sand through gravity-flotation combined separation

Abstract

The invention discloses a process for directly purifying quartz sand through gravity-flotation combined separation, and belongs to the technical field of deep processing of non-metallic ores. An existing acid leaching-roasting method is large in pollution and high in cost, and impurities such as Fe, Ti and Al are difficult to remove at the same time through single reselection or flotation. The method comprises the following steps: firstly, crushing raw ore, performing rod milling, and classifying by a cyclone until d90 is equal to 0.15 mm; then combined reselection is conducted through a two-section table concentrator and a centrifugal machine, pre-enriched concentrate with SiO2 larger than or equal to 99.2% is obtained, and the heavy mineral removal rate is larger than or equal to 65%; then, under different pH conditions, lauric acid, a neutral oil emulsified collecting agent and a mixed amine collecting agent are used for collecting mica and feldspar in a segmented mode, so that the grade of SiO2 is increased to be larger than or equal to 99.9%, and Al2O3 and Fe2O3 are reduced to be larger than or equal to 85% and larger than or equal to 70% relative to gravity concentrate; finally, deionized water washing and vacuum drying are conducted, and the high-purity quartz sand is obtained. The whole process is free of hydrofluoric acid and high-temperature roasting, the recovery rate of SiO2 with the size fraction of-0.6 + 0.1 mm is increased to 93-95%, product indexes are stable, equipment is conventional, and industrial popularization is easy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of deep purification of non-metallic minerals, and particularly relates to a method for purifying quartz by a two-stage combined process of "gravity separation-flotation". BACKGROUND

[0002] High-purity quartz (SiO2 purity≥99.9%) is an irreplaceable raw material for strategic emerging industries such as photovoltaic crucibles, semiconductor silicon wafers, and high-end optical glass. Therefore, efficient and green purification of ordinary quartzite (SiO2 95-97%) has become a core proposition that needs to be cracked in the field of non-metallic mineral processing.

[0003] The harmful impurities in quartz sand can be divided into two categories: (1) Fe and Ti oxides (hematite, rutile, etc.) with relatively large specific gravity; and (2) aluminosilicate gangue (feldspar, mica). These two types of minerals differ significantly in physical properties and surface chemical behavior, making it difficult to remove them simultaneously and efficiently by a single separation method. The traditional acid leaching process uses HF / HCl to dissolve Fe and Ti at high temperatures, which can increase the SiO2 grade to 99.99%, but generates a large amount of fluorine-containing waste acid, requires high corrosion-resistant equipment, and the fluorides in the fluorine-containing waste acid are highly toxic and bioaccumulative, can migrate over long distances and contaminate groundwater, cause soil calcification and crop death, and cause great harm to the human body. The roasting-water quenching-acid leaching method can further improve the exposure rate of impurities by phase transformation at 900-1000 ℃ to cause the explosion of inclusions, but the high energy consumption (≥350 kWh / t) and the increase in fine sand yield (-0.1 mm yield >35%) caused by particle cracking significantly increase the production cost.

[0004] Gravity separation is the first choice due to its environmental friendliness and low operating cost. The shaking table and spiral chute have good tailing throwing effect on Fe and Ti oxides with a particle size of +0.1 mm, but when the particle size is reduced to -0.1 mm, the particle settling Reynolds number Re<1, and the separation efficiency of traditional gravity separation equipment decreases sharply. The centrifugal separator can extend the effective recovery lower limit to 0.038 mm by strengthening the centrifugal force field (centrifugal intensity 60-120 g), but the density difference between quartz and feldspar is only 0.2 g / cm 3 , and single centrifugal separation cannot achieve high purification. The flotation method can deeply remove feldspar and mica by taking advantage of the surface chemical difference, but Fe and Ti oxides have similar surface charges to quartz under acidic conditions, resulting in synchronous floating, and the Fe2O3 content in the concentrate often stays at 0.02-0.04%, which cannot break through the photovoltaic threshold of 0.005%. In addition, the slime cover will significantly reduce the selectivity of amine collectors, and the reagent dosage is as high as 800-1200 g / t, the foam is sticky, and the operation stability is poor.

[0005] In recent years, the "gravity-flotation combined process" has become a research hotspot, but the existing research mostly uses gravity separation as a roughing method, and the separation size is usually set at 0.5-1 mm, which causes the Fe and Ti oxides that have been dissociated into single bodies to be mixed into the gravity separation concentrate again, the flotation load increases by 30-50%, and the final SiO2 recovery rate is still lower than 88%. On the other hand, the particle size, concentration and reagent system between gravity separation and flotation are not optimized in coordination, which leads to the need for high-temperature acid leaching as a "bottom-up" step in the flotation section, and the environmental problem has not been fundamentally solved.

[0006] Therefore, how to realize the efficient coupling of "gravity separation pre-concentration-flotation deep impurity removal" at normal temperature and pressure, break through the technical bottleneck of synchronous removal of fine-grained Fe and Ti oxides and aluminosilicates, and cancel the high-pollution acid washing link is a key scientific problem that has not been solved in the field of quartz sand purification, and is the starting point and core innovation of the present application. SUMMARY

[0007] In view of the above problems of the prior art, the present application aims to provide a gravity-flotation combined process for directly purifying quartz sand, so as to solve the problem that quartz and gangue are not easy to separate.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical route: (1) crushing, grinding and classification: crushing the raw ore to -2 mm, wet grinding by a rod mill to -0.6 mm, and classifying by a cyclone, with the overflow particle size controlled at d 90 =0.15 mm; The raw ore is suitable for quartzite and granite pegmatite type quartz ore with an initial SiO2 grade of 95-98%.

[0009] (2) gravity separation pre-concentration: using a "two-stage table + centrifugal concentrator" combined gravity separation, with the specific parameters being: a. roughing table: horizontal slope 1.8-2.2°, stroke 15-17 mm, stroke frequency 300-320 times / min; b. cleaning table: horizontal slope 1.2-1.5°, stroke 12-14 mm, stroke frequency 350-380 times / min; c. centrifugal concentrator: rotation speed 2200-2500 r / min, backflush water flow rate 1.8-2.2 L / min; The SiO2 grade of the gravity separation concentrate is ≥99.2%, and the removal rate of heavy minerals (Fe and Ti oxides) is ≥65%; (3) flotation deep impurity removal: Under the condition of pH=9.5-10.5, the collector is added to pre-catch mica, and then the pH is adjusted to 1.5-2.5 to catch feldspar, and after closed-circuit cleaning, a flotation concentrate with SiO2≥99.9% is obtained; wherein the first pH adjusting agent is soda ash, and the second pH adjusting agent is sulfuric acid or hydrochloric acid, and the collector and the amount are: 500-800 g / t lauric acid is added first to pre-catch mica with neutral oil emulsified collector, the neutral oil is one of kerosene or diesel, the ratio is 1:1-1:4; the emulsifier is a Tween series emulsifier, the amount is 2.5% of the weight of the collector; and then 60-100 g / t mixed amine (dodecylamine: octadecylamine = 6:4 to 8:2) is added to catch feldspar. After three cleaning, the tailings of each cleaning are returned to the previous operation to form a closed circuit; finally, a flotation concentrate with SiO2≥99.9% is obtained, and the impurity removal rate (relative to the cleaning concentrate) is Al2O3≥85%, Fe2O3≥70%; (4) washing and drying: the flotation product is washed with deionized water for 3 times, and the final high-purity quartz sand product is obtained after drying under vacuum. Deionized water is used for washing, and the total amount of Ca 2+ +Mg 2+ in the washing water is less than 10 mg / L.

[0010] By adopting the technical scheme of the present application, the SiO2 content in the final product is not less than 99.99%; Compared with the prior art, the high-purity quartz sand heavy-flotation combined purification method provided by the present application has the following remarkable beneficial effects: 1. Green and efficient full-physical deep purification is realized By the two-stage synergistic process of "gravity separation-flotation", the quartz sand is successfully purified to SiO2≥ 99.9% without using HF and other strong acids and high-temperature acid leaching, which realizes the replacement of the traditional high-pollution and high-energy-consumption acid leaching process. This not only completely avoids the generation of fluorine-containing waste acid and its serious harm to the environment and human body, but also greatly reduces the equipment corrosion requirement and subsequent environmental protection treatment cost, which is a clean and sustainable purification path.

[0011] 2. The connection and synergy of the two-stage heavy-flotation process are innovatively optimized By setting the effective boundary particle size to d 90 =0.15 mm, and adopting the combined gravity separation process of "two-stage shaking table+centrifugal concentrator", the removal efficiency of fine particle level (especially-0.1 mm) Fe, Ti and other heavy minerals is significantly improved (≥65%), which provides guarantee for the quality of the gravity separation concentrate (SiO2≥ 99.2%). This design avoids the problem that the dissociated fine particle impurities are mixed into the gravity separation concentrate and increase the flotation load in the traditional process, so that the impurity load of the subsequent flotation is reduced by 30-50%, and the efficiency and stability of the whole process are improved.

[0012] 3. Breakthrough in the technical bottleneck of simultaneous deep removal of fine Fe and Ti oxides and aluminosilicates. In the flotation stage, mica and feldspar are collected in stages using lauric acid and neutral oil emulsified collectors, along with mixed amine collectors. This selectively activates and enhances the collection of aluminosilicates such as feldspar and mica, while effectively suppressing the harmful flotation of Fe and Ti oxides due to their similar surface charges. The stepwise addition of combined collectors achieves highly selective collection of mica and feldspar with low reagent consumption (total reagent consumption is significantly lower than the 800-1200 g / t of traditional single-amine flotation). Ultimately, the Al2O3 removal rate in the flotation concentrate is ≥85%, and the Fe2O3 removal rate is ≥70%.

[0013] 4. Process parameters are optimized in a coordinated manner, resulting in strong operational stability. From crushing and classifying, to gravity separation equipment parameters (slope, stroke, speed, etc.), to flotation pulp concentration, pH value, reagent addition sequence and dosage, all processes have undergone systematic design and collaborative optimization. This integrated design ensures smooth connection between each link, stable and controllable process, and is conducive to continuous and stable industrial production. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0015] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The following embodiments are only used to illustrate this application and do not constitute a limitation on the claims.

[0016] Example 1 (1) Crushing and Classification: 100 kg of raw quartzite ore from Anhui Province (SiO2 97.8%, Fe2O3 0.18%, Al2O3 0.95%) was crushed to -2 mm by jaw crusher; wet-milled to -0.6 mm by rod mill (φ300×400 mm, steel rod filling rate 35%); classified by hydrocyclone (φ50 mm, inlet pressure 0.20 MPa), overflow d 90 =0.15 mm (measured by laser particle size analyzer).

[0017] (2) Gravity separation pre-enrichment: a. Roughing shaking table: transverse slope 2.0°, stroke 16 mm, stroke rate 310 times / min, yield of roughing concentrate 62.3%; b. Cleaning shaking table: transverse slope 1.3°, stroke 13 mm, stroke rate 365 times / min; c. Centrifuge (φ400 mm horizontal): rotation speed 2300 r / min, backwash water 2.0 L / min; gravity concentrate index: SiO2 99.23%, Fe2O3 0.065%, Al2O3 0.38%, heavy mineral removal rate 67.1%.

[0018] (3) Depth flotation for impurity removal: The pulp concentration was adjusted to 28 wt%, and the pH was adjusted to 9.5 with soda ash. 600 g / t of lauric acid and neutral oil emulsified collector were added to pre-collect mica, where the neutral oil was kerosene in a ratio of 1:2 and pine oil was 20 g / t. Mica flotation was carried out in a roughing and cleaning process. Then, the pH was adjusted to 2.2 with H2SO4, and 80 g / t of mixed amine (dodecylamine:octadecylamine = 7:3) was added to carry out feldspar flotation in a roughing and cleaning process. The final flotation concentrate had the following composition: SiO2 99.92%, Fe2O3 0.018%, and Al2O3 0.055%. Compared with the gravity concentrate, the Al2O3 removal rate was 85.5% and the Fe2O3 removal rate was 72.3%.

[0019] (4) Washing and drying: Washed three times with deionized water (liquid-solid ratio 3:1), and vacuum dried at 80 ℃ for 4 h to obtain 92.4 kg of high-purity quartz sand.

[0020] Example 2 In Example 2, only the carbon chain ratio of the collector "mixed amines" in the flotation circuit was adjusted using a single factor: the molar ratio of dodecylamine to octadecylamine was changed from 7:3 to 6:4, while the remaining crushing, gravity separation, washing, and drying processes remained completely consistent with Example 1. This fine-tuning increased the molar fraction of octadecylamine in the mixed amines from 30% to 40%, increased the average carbon chain length from 13.2 to 14.1, slightly decreased the SiO2 grade of the flotation concentrate to 99.90%, and reduced the removal rates of Al2O3 and Fe2O3 by 1.8% and 1.5%, respectively. However, due to the increased hydrophobic end of octadecylamine, the probability of adhesion between the target mineral and bubbles increased, resulting in a 0.9% increase in concentrate yield compared to Example 1. This demonstrates the feasibility of "trading purity for recovery," providing an economical alternative for the subsequent production of high-purity quartz sand.

[0021] Example 3 Example 3 kept the process framework unchanged, only increasing the centrifuge speed from 2300 r / min to 2400 r / min, while slightly decreasing the backwash water flow rate from 2.0 L / min to 1.9 L / min, to investigate the effect of centrifugal separation intensity on heavy mineral removal rate and subsequent flotation parameters. The increased speed increased the centrifugal acceleration from 328 g to 378 g, and the bed compaction increased by 0.04 g / cm, resulting in an increase in the ratio of centrifugal force to radial flow film shear force on heavy minerals (chromite, ilmenite, zircon, etc.) from 1.25 to 1.42, increasing the heavy mineral capture probability by 2.7%, and increasing the heavy mineral removal rate of the gravity concentrate from 67.1% to 68.9%. However, due to the 0.8 mm increase in bed thickness, some quartz particles with a size between 30-40 µm were misplaced into the heavy phase, causing the SiO2 grade of the gravity concentrate to only slightly increase from 99.23% to 99.31%. The mechanically entrained impurities were effectively removed in the subsequent flotation stage, and the final SiO2 grade of the high-purity sand still reached 99.91%, which was the same as in Example 1. This shows that moderately increasing the centrifugal separation intensity can improve the removal efficiency of heavy minerals without sacrificing the final purity, which is of positive significance for reducing the reagent burden in the flotation stage.

[0022] Example 4 To further verify the applicability of the "gravity-flotation combined separation" process to low-grade silicon raw materials, Example 4 replaced the raw ore with a granite pegmatite-type quartz deposit in Jiangsu Province. The genesis of this ore body differs significantly from that of the quartzite-type deposit in Anhui Province: the SiO2 content is only 96.5%, the Al2O3 and Fe2O3 contents are 2.1% and 0.24% respectively, and the aluminosilicates such as feldspar and mica are disseminated in a disseminated manner with uneven particle size. The experiment followed the crushing-grinding-gravity separation-flotation process of Example 1, only shortening the rod milling time by 5% based on the disseminated characteristics of the raw ore, thus reducing the overflow d 90 The grinding diameter was reduced from 0.15 mm to 0.14 mm to minimize the risk of over-grinding. In the gravity separation stage, after two cycles of shaking table and centrifuge, the SiO2 grade of the concentrate increased to 99.20%, indicating that gravity separation has a good pre-enrichment effect on feldspar and ferrous minerals. In the flotation stage, under the same reagent regime, due to the high aluminum impurity content of the raw ore, the absolute removal of Al2O3 reached 1.97%, with a removal rate of 91.4%, significantly better than Example 1; the final concentrate SiO2 grade reached 99.93%, exceeding the level of Example 1. These results experimentally confirm that the "gravity-flotation combined separation" technology platform constructed in this study is equally efficient for low-grade granite pegmatite-type quartz deposits, providing technical support for expanding the boundaries of usable silicon resources and alleviating the shortage of high-purity quartz sand raw materials.

[0023] Example 5 A single-factor control design was adopted, eliminating the gravity separation pre-enrichment stage and directly adjusting the -0.6 mm stage overflow into the flotation process. The remaining adjustment concentration, pH, reagent regime, and flotation procedure were completely consistent with Example 1 to quantitatively evaluate the coupling effect of gravity-flotation. Due to the lack of pre-removal of heavy minerals and iron particles by gravity separation, the Fe2O3 and Al2O3 contents in the flotation feed were as high as 0.18% and 0.95%, respectively, and the content of heavy mineral inclusions such as ilmenite and chromite in the -40 µm particle size increased by 1.7 times. Under strongly acidic conditions (pH=2.2), the selectivity of mixed amines for adsorption of oxide films on the surface of heavy minerals decreased, causing some iron and titanium impurities to float simultaneously with feldspar; the final flotation concentrate SiO2 grade was only 98.7%, and Fe2O3 and Al2O3 were 0.12% and 0.48%, respectively, far below the 99.9% high-purity sand requirement. This comparative example demonstrates from the opposite perspective that the gravity separation stage can not only directly remove more than 67% of heavy minerals, but also significantly reduce the impurity load of subsequent flotation and improve flotation selectivity. It is an irreplaceable key link in the entire process chain, indicating that the "gravity-flotation combined separation" strategy plays a crucial role in the preparation of high-purity quartz sand.

[0024] Example 6 This comparative example follows the same crushing, classification, gravity separation pre-enrichment, washing, and drying processes and parameters as in Example 1. The key adjustment is to the collector scheme in the deep flotation impurity removal stage. The collector and related steps of this invention are eliminated, and a traditional single-amine flotation reagent system is adopted instead. Specifically, the collector addition operation is changed; 900 g / t of dodecylamine (DDA) is added as a single collector, along with 20 g / t of pine oil as a frother. This reagent dosage is based on the typical range (800-1200 g / t) for traditional single-amine flotation of quartz sand. The resulting flotation concentrate has the following chemical composition: SiO2 content 99.56%, Fe2O3 content 0.041%, and Al2O3 content 0.21%. Compared to the gravity separation concentrate, the Al2O3 removal rate is 44.7%, and the Fe2O3 removal rate is 36.9%. Compared with the flotation results of Example 1 (the method of the invention), the conventional single amine flotation scheme used in this comparative example has significant shortcomings. First, the product purity is substandard: the final quartz sand product has a SiO2 grade of only 99.56%, and the content of Al2O3 and Fe2O3 impurities is significantly higher than that obtained by the method of the invention. Second, the reagent dosage is high and the selectivity is poor: although the total amine dosage (900 g / t) is lower than the upper limit reported in the traditional method, it is still significantly higher than the total dosage of the combined collector added stepwise in this invention (in Example 1, the total dosage of amines and sulfonates was 350 g / t, and the mixed amine was 80 g / t, for a total of 430 g / t). Third, it cannot replace acid leaching: this result further proves that without the optimized combined collection and activation strategy of this invention, relying solely on "gravity separation + traditional single amine flotation" cannot purify quartz to more than 99.9% at room temperature and pressure. It still requires high-pollution and high-energy-consumption deep acid leaching as a "backup" step, and cannot achieve the goal of green purification using a fully physical method.

Claims

1. A purification method of high purity quartz sand by gravity separation and floatation, characterized by, The method comprises the following steps: (1) Grading by crushing and grinding: the quartz ore is crushed to below 2 mm, wet ground to below 0.6 mm, and classified by a cyclone, with the overflow particle size d 90 = 0.15 mm controlled; (2) Re-election pre-enrichment: two-stage shaking table and centrifuge combined re-election, SiO2≥99.2% of the re-election concentrate is obtained; (3) Flotation depth impurity removal: under the condition of pH = 9.5-10.5, first add collector to pre-catch mica, then adjust pH to 1.5-2.5 to catch feldspar, after closed-circuit cleaning, SiO2≥99.9% of the flotation concentrate is obtained; (4) Washing and drying: the flotation product is washed by deionized water and vacuum dried to obtain high-purity quartz sand.

2. The method of claim 1, wherein, In step (1), the hydrocyclone is used for classification, and the inlet pressure is 0.18-0.22 MPa.

3. The method of claim 1, wherein, In step (2), the shaking table includes a roughing shaking table and a cleaning shaking table: Roughing shaking table: horizontal slope 1.8-2.2°, stroke 15-17 mm, stroke frequency 300-320 times / min; Cleaning shaking table: horizontal slope 1.2-1.5°, stroke 12-14 mm, stroke frequency 350-380 times / min.

4. The method of claim 1, wherein, In step (2), the centrifuge is a horizontal centrifugal concentrator, the rotating speed is 2200-2500 r / min, the backflush water flow is 1.8-2.2 L / min, and the drum diameter is 400-600 mm.

5. The method of claim 1, wherein, In step (3), the pulp concentration is 25-30 wt%; the amount of activator is: sodium fluosilicate 400-600 g / t, aluminum sulfate 200-300 g / t.

6. The method of claim 1, wherein, In step (3), the first pH adjuster is soda ash, the second pH adjuster is sulfuric acid or hydrochloric acid, and the collector and its amount are: First add 500-800 g / t lauric acid and neutral oil emulsion collector to pre-catch mica, the neutral oil is one of kerosene or diesel, the ratio is 1:1-1:4; the emulsifier is a Tween series emulsifier, the amount is 2.5% of the weight of the collector; then add 60-100 g / t mixed amine to catch feldspar.

7. The method of claim 6, wherein, The mixed amine is a mixture of dodecylamine and octadecylamine, wherein the mass ratio of dodecylamine to octadecylamine is 6:4 to 8:

2.

8. The method of claim 1, wherein, Step (3) also includes adding 15-25 g / t of pine oil as a foaming agent.

9. The method of claim 1, wherein, Ca 2+ with Mg 2+ total amount less than 10 mg / L.

10. The method according to any one of claims 1 to 9, characterized in that, The SiO2 content in the final product is not less than 99.99%; the removal rate of Fe and Ti oxides in the heavy minerals removed in the re-election section is not less than 65%; the removal rate of Al2O3 in the flotation section is not less than 85%, and the removal rate of Fe2O3 is not less than 70%.

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