Process for preparing and processing weathered granite into high-purity quartz sand

Abstract

The application belongs to the field of non-metallic mineral deep processing, and particularly relates to a process for preparing and processing high-purity quartz sand from weathered granite. The technical scheme of the application comprises the following steps: (1) crushing and finely grinding the weathered granite to a particle size of -0.2 mm; (2) performing gravity separation with a one-stage shaking table; (3) magnetic separation; (4) performing two-stage reverse flotation on the magnetic separation product with two kinds of anionic and cationic collectors, namely dodecylamine and sodium dodecylsulfate (SDS), and using lauryl betaine as a synergist; (5) adjusting the pH of the ore slurry to 11-12 with NaOH, and performing positive flotation with three kinds of anionic and cationic collectors, namely dodecylamine, sodium oleate and SDS, and using CaCl2 as a quartz activator, and additionally using lauryl betaine as a synergist; (6) calcining and water quenching; and (7) obtaining high-purity quartz sand with a SiO2 content of more than 99.96% by heating leaching with a mixed acid of H2SO4+HCl+HNO3+HF. The application provides an economic and efficient method for high-value utilization of low-grade weathered granite.

Description

Technical Field

[0001] This invention belongs to the field of deep processing of non-metallic minerals, specifically relating to a process for preparing high-purity quartz sand using weathered granite. Background Technology

[0002] Quartz is widely distributed in nature, but deposits capable of producing high-purity quartz are extremely scarce. Therefore, effectively purifying and processing high-purity quartz from natural siliceous raw materials has always been a research hotspot in the field of non-metallic mineral processing. Granite quartz has a low quartz content (20-30%), with impurities such as quartz, kaolinite, mica, and feldspar accounting for as much as 80% of the ore. Although granite deposits are mostly large and super-large, there are currently no mines that develop granite quartz with quartz as the primary mineral. This type of quartz is mainly utilized as a co-existing mineral resource or tailings, resulting in a relatively low overall utilization rate.

[0003] Currently, there are reports on the preparation of high-purity quartz sand using granite under laboratory conditions. Wei Dongdong et al. (application number 202010923980.8) disclosed a process using washing-crushing sand making-calcination-grinding-magnetic separation-flotation to obtain high-purity quartz products with SiO2 content ≥99.9%. Chen Jian et al. (application number 202211477041.0) disclosed a process using calcination-water quenching, crushing-screening, flotation and acid washing to obtain high-purity quartz sand with 3N6 or higher, using flotation reagents including polyetheramine, dodecylamine, oil-based propylene diamine, and octadecylamine. Zhang Haiqi et al. (application number 202111131277.4) disclosed a method for obtaining 4N5 grade high-purity quartz products by using crushing, grinding and classification, gravity separation, magnetic separation, acidic positive flotation with dodecylamine as a collector, calcination-water quenching, ultrasonic acid leaching, and thermal leaching. Tian Huiming et al. (application number 202210778924.9) used natural granite pegmatite as raw material and obtained high-purity quartz sand with a purity of 4N or higher through crushing, grinding, magnetic separation, color separation, acid washing, flotation, heavy liquid separation, and high-temperature chlorination. Li Yubiao (application number 202010721757.5) disclosed a method for preparing 4N grade high-purity quartz sand using pegmatite quartz as raw material through crushing, grinding, screening, flotation, high-temperature roasting, water quenching, and hot-press leaching. However, the purification processes used in existing literature include at least one calcination, heated leaching, hot-press leaching, and high-temperature chlorination, among other deep purification methods. The flotation process has failed to achieve a purity level of 3N.

[0004] Flotation is an essential process in quartz purification and a crucial step in removing impurity minerals. The challenges in flotating granite lie in its low mineral content, low degree of monomer liberation, severe mud formation, and small difference in floatability between quartz and impurity minerals. Traditional cationic collectors such as amines (e.g., dodecylamine) and anionic collectors such as fatty acids (e.g., sodium oleate) struggle to effectively separate quartz from silicate impurities. In terms of improving collector performance, combined reagent methods show promising development prospects, with significant advantages including a wide range of raw material sources, simple processes, and high flexibility. When different reagents are used in combination in certain proportions, they work synergistically on the mineral surface, achieving a "1+1>2" effect. Therefore, developing economical and efficient enhanced flotation separation technologies is imperative. Summary of the Invention

[0005] To address the widespread problem of inferior quality in high-quality granite resources, this invention provides a combined crushing-grinding-gravity separation-magnetic separation-flotation-leaching process for purifying and processing high-purity quartz sand. The process flow is as follows: Figure 1 As shown.

[0006] The technical solution for achieving the objective of this invention includes the following steps:

[0007] (1) A three-stage closed-circuit crushing process is adopted. The granite sample is crushed by a large jaw crusher and then finely crushed by a small jaw crusher. The crushed product is obtained by screening to a particle size of -2mm. The crushed product is then dry-ground to a particle size of -0.2mm by closed-circuit grinding.

[0008] (2) Under the condition of slurry concentration of 10~30%, a single-stage shaking table (XZY-1600×700mm) is used for gravity separation to remove chlorite, microcline, muscovite and albite.

[0009] (3) Under the conditions of slurry concentration of 10~30% and magnetic field strength of 1~1.5T, a wet high-intensity magnetic separator or an electromagnetic high-gradient magnetic separator is used to perform two-stage magnetic separation on the shaking table concentrate to remove magnetic impurity minerals.

[0010] (4) In a single-cell flotation machine, the pH of the pulp is adjusted to 2.0~3.0 with HF, i.e. hydrofluoric acid. Under the conditions of pulp concentration of 10~30% and main machine speed of 1700~2100 r / min, two cationic and anionic collectors, dodecylamine and sodium dodecyl sulfonate, are used, along with 0.01mM~0.1mM molar concentration of amphoteric surfactant lauryl betaine as an synergist to perform two-stage reverse flotation on the magnetic concentrate to remove feldspar impurities.

[0011] (5) In a single-cell flotation machine, the pulp is adjusted to pH 11-12 with NaOH, and a combination of three anionic and cationic collectors, namely dodecylamine, sodium dodecyl sulfonate and sodium oleate, is used. CaCl2 is used as a quartz activator, and 0.01mM-0.1mM lauryl betaine is added as an synergist to remove mica, kaolinite and amphibole impurities by positive flotation. The flotation concentrate is washed 5-10 times with ultrapure water and dried to obtain 3N grade quartz sand.

[0012] (6) Weigh a certain mass of flotation concentrate and put it into a quartz crucible. Place it in a muffle furnace at 800~1100℃ and calcine for 1~2 h. Then quickly take out the calcined material and place it in ultrapure water to expose the inclusions on the quartz surface. Wash the calcined product with ultrapure water 5~10 times.

[0013] (7) The product after water quenching is heated and stirred at around 90°C for 2-6 hours to remove the leachate. The product is then washed with ultrapure water 5-10 times and dried to obtain high-purity quartz sand with a SiO2 content of over 99.96%.

[0014] The weathered granite mentioned above is a low-grade granite with a quartz content of 20-30%, a high degree of weathering, and large grains.

[0015] The lauryl betaine mentioned is an amphoteric surfactant with the molecular formula C16H33NO2 and a molecular structure as shown below. Figure 2 As shown.

[0016] The features and beneficial effects of this invention are as follows: a process for preparing high-purity quartz sand using low-grade weathered granite, wherein the granite ore is processed through a purification process including crushing, closed-circuit grinding, shaking table, reverse flotation-direct flotation, calcination and water quenching, and acid leaching, to obtain high-purity quartz sand with an SiO2 content of over 99.96%. Specifically, after pretreatment by crushing, grinding, and shaking table impurity removal, the superhydrophilic effect of the amphoteric surfactant lauryl betaine on quartz significantly improves the collecting ability and selectivity of dodecylamine and SDS for quartz minerals, thereby enabling the purity of the flotation product to directly reach the 3N level or above. Its mechanism of action is that lauryl betaine selectively adsorbs onto the surface of quartz minerals, reducing the hydrophilic contact angle of the quartz mineral surface to near zero, which greatly increases the inhibition effect of quartz in the flotation stage; on the other hand, as an amphoteric surfactant, lauryl betaine, in combination with dodecylamine, SDS, and sodium oleate, increases the adsorption of the collector on the mineral surface, thereby improving the collecting ability of quartz minerals.

[0017] The synergist lauryl betaine involved in this invention is an amphoteric surfactant with advantages such as low price, stable properties, and no pollution. Furthermore, when used in amounts less than 0.1 mM, it does not cause pollution problems related to metal ions or organic matter in the quartz purification system. This method has advantages such as small dosage, cleanliness and environmental friendliness, low cost, and good enhancement indicators. It significantly improves the enrichment ratio and impurity removal rate of quartz flotation, providing a new approach for subsequent deep purification and preparation of high-value quartz products. It also has certain reference value for the fine processing of other types of granite. Attached Figure Description

[0018] Figure 1 A flowchart illustrating the purification and processing technology of weathered granite;

[0019] Figure 2 This is the molecular structure diagram of lauryl betaine;

[0020] Figure 3 XRD analysis diagram of the raw ore;

[0021] Figure 4 This is a flow chart of the flotation separation process. Detailed Implementation Plan Example

[0022] (1) Representative weathered granite (hereinafter referred to as granite) ore samples were collected from Fuzhou, Jiangxi Province. The results of multi-element analysis of the raw ore are shown in Table 1; the results of X-ray diffraction analysis are shown in Table 2. Figure 3 As shown. The raw ore has a low SiO2 content, only 73.64%, and the main impurity elements are Al, Fe, K, and Na. It also contains certain amounts of Ti, Mg, Mn, Ca, and S, as well as trace elements such as Pb, Sr, Y, Zr, Zn, Ga, and Nb. The weathered granite has a very low quartz content, only 24.09%, and contains impurity minerals such as microcline, albite, muscovite, and kaolinite.

[0023] Table 1. Elemental analysis results of the raw ore (%)

[0024]

[0025] (2) A three-stage closed-circuit crushing process is adopted. After the granite sample is crushed by a large jaw crusher, it is further crushed by a small jaw crusher and then screened to obtain a -2mm particle size crushed product. The crushed product is then dry-ground to a -0.1mm particle size grinding product by closed-circuit grinding.

[0026] (3) Magnetic separation was performed on the -0.1mm grinding product under the conditions of feed concentration of 30% and magnetic field strength of 1T and 1.5T respectively to obtain magnetic concentrate with SiO2 content of 74.31%, Al2O3 content of 15.38%, Fe2O3 content of 0.43% and K2O content of 5.08%.

[0027] (4) Take 50g of mineral sample into a 500mL flotation cell, add deionized water, stir for 3min, add HF or NaOH to adjust the pH of the pulp, and add the collector (dodecylamine, sodium dodecyl sulfonate SDS, sodium oleate), activator (CaCl2), and amphoteric surfactant (lauryl betaine) in sequence for each flotation. Stir for 3min after each addition of reagents and float for 3min. The flotation process is as follows: Figure 4 As shown, the flotation reagent system and flotation results are shown in Tables 2 and 3, respectively.

[0028] Table 2 Comparison of flotation reagent systems for three different flotation schemes

[0029]

[0030] Table 3 Comparison of flotation results for three different flotation schemes

[0031]

[0032] The effects of two-stage reverse flotation and two-stage reverse flotation-direct flotation on impurity removal were compared. Results showed that with HF dosage of 40 mM (pH 2.0–3.0), using dodecylamine and SDS as collectors, a single reverse flotation stage yielded a flotation concentrate with a yield of only 36.27% and a concentrate grade of only 92.77%. Further flotation of the reverse flotation concentrate using a combination of dodecylamine, sodium oleate, and SDS as collectors, followed by direct flotation, yielded a flotation concentrate with a yield of 35.94% and a concentrate grade of 96.18%. Comparison of Scheme I and Scheme II showed that single reverse flotation was ineffective for removing impurities from magnetically separated concentrates with low quartz content; however, a two-stage reverse flotation-direct flotation process effectively improved the purification effect.

[0033] Comparing the results of schemes II and III, it is evident that the addition of the amphoteric surfactant lauryl betaine significantly improved the purification efficiency of quartz minerals, and high-purity quartz products of grade 3N or higher could be directly obtained by flotation. The main impurity, Al, could be reduced from 15.38% to 0.035%, with an Al removal rate as high as 99.93%.

[0034] The enhancing mechanism of quartz flotation by the amphoteric surfactant lauryl betaine is as follows: On the one hand, the emulsifying effect of lauryl betaine can improve the dispersion of the collector and has a synergistic effect with the collector molecules, thereby enhancing the adsorption of the collector on the surface of quartz minerals and improving the collection capacity of quartz in the forward flotation stage; on the other hand, lauryl betaine selectively adsorbs on the surface of quartz minerals, reducing the hydrophilic contact angle of the quartz mineral surface to near zero, which greatly increases the inhibition effect of quartz in the reverse flotation stage.

[0035] (5) Weigh a certain mass of flotation concentrate, place it in a quartz crucible, and calcine it in a muffle furnace at a temperature of 1000℃ for 2 hours. After calcination, quickly pour the sample into ultrapure water for water quenching. The "calcination-water quenching" process exposes mineral and fluid inclusions in the quartz due to thermal stress, and also allows elements such as Al, Li, Na, and K in the crystal lattice to accumulate on the quartz surface under high-temperature phase transformation, which is beneficial for subsequent leaching to remove impurities.

[0036] (6) The water-quenched sample was washed, dried, and cooled repeatedly with ultrapure water and then used as a leaching sample. A certain amount of leaching sample was placed in a clean polytetrafluoroethylene beaker, and a mixed acid mixture of H2SO4 (0.25 mol / L) + HCl (0.5 mol / L) + HNO3 (0.25 mol / L) + HF (0.5 mol / L) was added. The leaching was carried out for 4 h at a pulp concentration of 10%, a temperature of 90℃, and a stirring speed of 300 rpm. After leaching, the leachate was removed, the leaching concentrate was taken out, and the product was washed repeatedly with ultrapure water 5-10 times and then dried. The final quantitative analysis results of impurity elements in the purified product are shown in Table 4. The results showed that the SiO2 content of the leaching concentrate reached 99.96%, and the total impurity content was 388.42 µg / g.

[0037] Table 4. Multi-element analysis results of the leaching concentrate (µg / g)

[0038]

[0039] Example 2

[0040] (1) Representative weathered granite samples were collected from Fuzhou, Jiangxi Province. The results of multi-element analysis and X-ray diffraction analysis of the raw ore are shown in Table 1 of Example 1, respectively. Figure 3 As shown.

[0041] (2) A three-stage closed-circuit crushing process is adopted. After being crushed by a large jaw crusher, the product is further crushed by a small jaw crusher and screened to obtain a -2mm particle size crushed product. The crushed product is then dry-ground in a closed-circuit grinding process to a particle size of 0.1~0.2mm.

[0042] (3) Gravity separation was performed using a shaking table (XZY-1600×700mm), and the separation results are shown in Table 5. It can be seen that the SiO2 content of the 0.1-0.2mm particle size sample increased from 77.67% to 78.78% after shaking table separation. The impurity element Al was mainly concentrated in the fine-grained segment of the shaking table, while the impurity element Fe was almost entirely concentrated in the coarse-grained tailings end. The removal rate of Fe element was as high as 60%, and the removal effect was very significant. The fine-grained tailings of the shaking table were mainly chlorite, microcline, muscovite, and albite; the coarse-grained tailings of the shaking table were mainly albite.

[0043] Table 5. Sorting results of 0.1-0.2mm granite on shaking table

[0044] (4) Magnetic separation was performed on the shaking table concentrate at a feed concentration of 30% and magnetic field strengths of 1T and 1.5T, respectively, to obtain a magnetic concentrate with SiO2 content of 79.46%, Al2O3 content of 11.85%, Fe2O3 content of 0.14%, and K2O content of 4.8%. The test results of the mineralogical parameters of the magnetic concentrate by the automatic measurement system (BGRIMM Process Mineralogy Analyzer) showed that the quartz mineral content was only 47.27%, the feldspar content was 44.01%, the kaolinite content was 6.81%, and the muscovite content was 0.95%.

[0045] (5) Take 50g of mineral sample into a 500mL flotation cell, add deionized water, stir for 3min, add HF or NaOH to adjust the pH of the pulp, and add the collector (dodecylamine, sodium dodecyl sulfonate SDS, sodium oleate), activator (CaCl2), and amphoteric surfactant (lauryl betaine) in sequence for each flotation. Stir for 3min after each addition of reagents and float for 3min. The flotation process and flotation reagent system are as described in Example 1. Figure 2 As shown in Table 2. The flotation results are shown in Table 6.

[0046] Table 6 Comparison of flotation results for three different flotation schemes

[0047] The effects of two-stage reverse flotation and two-stage reverse flotation-direct flotation on impurity removal were compared. Results showed that with HF dosage of 40 mM (pH 2.0–3.0), using dodecylamine and SDS as collectors, a single reverse flotation stage yielded a concentrate with a yield of 61.34% and a grade of only 89.56%. Further flotation of the reverse flotation concentrate using a combination of dodecylamine, sodium oleate, and SDS as collectors, followed by direct flotation, yielded a concentrate with a yield of 36.95% and a grade of 97.12%. Comparison of Scheme I and Scheme II showed that single reverse flotation was ineffective for removing impurities from magnetic concentrate with a quartz content of only 47.27%, and the purification effect could be effectively improved by a two-stage reverse flotation-direct flotation process.

[0048] Comparing the results of schemes II and III, it is evident that the addition of the amphoteric surfactant lauryl betaine significantly improves the purification efficiency of quartz minerals, and high-purity quartz products of grade 3N7 or higher can be directly obtained by flotation. The main impurity, Al, can be reduced from 11.85% to 0.1%, with an Al removal rate as high as 99.69%.

[0049] (6) Weigh a certain mass of flotation concentrate, put it into a quartz crucible, and calcine it in a muffle furnace at a temperature of 1000℃ for 2 hours. After calcination, quickly pour the sample into ultrapure water for water quenching.

[0050] (7) The water-quenched sample was washed, dried, and cooled repeatedly with ultrapure water and then used as a leaching sample. A certain amount of leaching sample was placed in a clean polytetrafluoroethylene beaker, and a mixed acid mixture of H2SO4 (0.25 mol / L) + HCl (0.5 mol / L) + HNO3 (0.25 mol / L) + HF (0.5 mol / L) was added. The leaching was carried out for 4 h at a pulp concentration of 10%, a temperature of 90℃, and a stirring speed of 300 rpm. After leaching, the leachate was removed, the leaching concentrate was taken out, and the product was washed repeatedly with ultrapure water 5-10 times and then dried. The final quantitative analysis results of impurity elements in the purified product are shown in Table 7. The results showed that the SiO2 content of the leaching concentrate reached more than 99.97%, and the total impurity content in the sample was 290.21 µg / g.

[0051] Table 7. Multi-element analysis results of the leaching concentrate (µg / g)

[0052]

Claims

1. A process for preparing high-purity quartz sand from weathered granite, characterized in that, The process includes: S1. After the granite is crushed by a crusher, it is screened to obtain a crushed product with a particle size of -2mm. The crushed product is then dry-ground in a closed-circuit grinding process to a grinding product with a particle size of -0.2mm. S2. Under certain slurry concentration conditions, gravity separation is carried out using a single-stage shaking table to remove chlorite, microcline, muscovite and albite. S3. Under certain conditions of slurry concentration and magnetic field strength, a magnetic separator is used to perform magnetic separation on the shaking table concentrate to remove magnetic impurity minerals. S4. In a single-cell flotation machine, the pH of the pulp is adjusted using HF (hydrofluoric acid). Under certain pulp concentration and main unit speed conditions, two cationic and anionic collectors, dodecylamine and sodium dodecyl sulfonate, are used, along with a certain molar concentration of the amphoteric surfactant lauryl betaine as an synergist. This is used to perform two-stage reverse flotation on the magnetic concentrate to remove feldspar impurities. The lauryl betaine has the molecular formula C16H33NO2 and its molecular structure is... ； S5. In a single-cell flotation machine, the pulp is adjusted to pH 11-12 with NaOH. A combination of three cationic and anionic collectors—dodecylamine, sodium dodecyl sulfonate, and sodium oleate—is used, with CaCl2 as a quartz activator and lauryl betaine (0.01-0.1 mM molar concentration) added as an synergist. Positive flotation is then used to remove mica, kaolinite, and amphibole impurities. The flotation concentrate is washed 5-10 times with ultrapure water and dried to obtain 3N grade quartz sand. S6. Weigh a certain mass of 3N grade quartz sand and put it into a quartz crucible. Place it in a muffle furnace at 800~1100℃ and calcine for 1~2 hours. Then, quickly take out the calcined material and place it in ultrapure water to expose the inclusions on the quartz surface. Wash the calcined product with ultrapure water 5~10 times. S7. The water-quenched product is leached by heating and stirring with a mixed acid of H2SO4 + HCl + HNO3 + HF for 2-6 hours. The leachate is removed, the leached product is washed with ultrapure water, and dried to obtain high-purity quartz sand with a SiO2 content of over 99.96%.

2. The process for preparing high-purity quartz sand from weathered granite as described in claim 1, characterized in that, The pulp concentration in S2 is 10~30%, and gravity separation is performed using a single-stage shaking table XZY-1600×700mm.

3. The process for preparing high-purity quartz sand from weathered granite as described in claim 1, characterized in that, Under the conditions of a slurry concentration of 10-30% and a magnetic field strength of 1-1.5T as described in S3, a wet high-intensity magnetic separator or an electromagnetic high-gradient magnetic separator is used to perform two-stage magnetic separation on the shaking table concentrate to remove magnetic impurity minerals.

4. The process for preparing high-purity quartz sand from weathered granite as described in claim 1, characterized in that, As described in S4, the slurry is adjusted to pH 2.0~3.0 with HF. Under the conditions of slurry concentration of 10~30% and main engine speed of 1700~2100 r / min, two cationic and anionic collectors, dodecylamine and sodium dodecyl sulfonate, are used, along with 0.01mM~0.1mM molar concentration of amphoteric surfactant lauryl betaine as an synergist. The magnetic concentrate is subjected to two-stage reverse flotation to remove feldspar impurities.

5. The process for preparing high-purity quartz sand from weathered granite as described in claim 1, characterized in that, S7 describes using a mixed acid mixture of H2SO4 + HCl + HNO3 + HF to heat and stir the water-quenched product at 90℃ for 2-6 hours. After removing the leachate, the product is washed with ultrapure water 5-10 times and dried to obtain high-purity quartz sand with a SiO2 content of over 99.96%.

6. The process for preparing high-purity quartz sand from weathered granite as described in claim 1, characterized in that, The weathered granite mentioned above is a low-grade granite with a quartz content of 20-30%, a high degree of weathering, and large grains.

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