Abstract
The low removal efficiency of fine clay impurities in natural powder quartz (NPQ) is the main problem that affects the practical utilization of this natural resource. In this work, detailed characterizations of NPQ and clay impurities in NPQ were analyzed by SEM-EDS, mineral liberation analysis (MLA) and impurities distribution analysis. A combined physical purification process, including sieving, scrubbing and centrifugation, was applied to remove the clay impurities. It was observed that the fine clay impurities adhering on quartz surface were effectively liberated by scrubbing, and the content of Fe2O3 and Al2O3 in the concentrate decreased from 0.48% and 0.40% to less than 0.01% and 0.02% at pH 9.3 or when the dosage of sodium hexametaphosphate (SHMP) was 1 × 103 g/t. The coagulation interaction between quartz and impurities including hematite and orthoclase were analyzed based on the classical Deyaguin-Landau-Verwey-Overbeek (DLVO) theory. The results indicated that the main coagulation affecting the separation efficiency was the heterocoagulation between quartz and impurities and homocoagulation among hematite particles. Furthermore, adding regulators such as sodium hydroxide (NaOH) or SHMP could significantly decrease the zeta potential of minerals and thus increase the total interaction energy (VT), which could effectively improve the dispersion of these fine impurity particles, and consequently improve the removal efficiency of impurities. Reverse increase of the zeta potential of minerals in strongly alkaline solutions or excessive SHMP were detected, which was likely the main factor limiting the further improvement of the purification efficiency.
Highlights
Quartz is a highly critical and strategic material for advanced and emerging industrial technologies, which can be used extensively in advanced manufacturing of materials such as optical fibers, semi-conduct materials, highly pure glass in aerospace, etc. [1,2]
In order to analyze the distribution of impurities in different sizable fractions, natural powder quartz (NPQ) were first sieved using a set of standard screens (100, 200 and 325 mesh), and the part of −325 mesh was divided into sediment and suspension by centrifugation at 315 rpm for 1 min
The results showed that the VT of O–O and orthoclase and hematite (O–H) were both positive, while the VT of hematite and hematite (H–H) was negative over the whole separation distance, which indicated that the coagulation of fine particles occurred mainly by the formation of homocoagulation between H–H in the slurry
Summary
Quartz is a highly critical and strategic material for advanced and emerging industrial technologies, which can be used extensively in advanced manufacturing of materials such as optical fibers, semi-conduct materials, highly pure glass in aerospace, etc. [1,2]. Among different natural quartz resources, crystal is still the first choice for high purity quartz preparation. High purity crystal resources are rare in the world. Researchers have tried to purify other natural quartz resources such as quartzite, quartz sand and white sand as substitutes [3,4]. In order to remove impurities, various processing methods were used. Physical methods such as magnetic separation, reverse flotation [5,6], and chemical treatment such as acidic leaching by hydrogen fluoride (HF) combined with other different fractions strong industrial acids such as HCl, HNO3 or H2 SO4 [2,7] were usually employed. Because of the scarcity of high-quality resources and the high processing costs, developing feasible and economical processing technology is especially important
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