Preparation of High-Purity Quartz by Roasting–Water Quenching and Ultrasound-Assisted Acid Leaching Process

High-purity quartz is a key material for photovoltaics, semiconductors, and optical fibers. The raw material for high-purity quartz mainly comes from natural crystal and pegmatite. It is an attractive research field to excavate alternative feedstocks for traditional materials. Quartz conglomerate is a coarse-grained, clastic sedimentary rock that is cemented by a secondary silica or siliceous matrix. Economically, quartz conglomerate is gaining attention as a strategic alternative to depleting high-grade quartz veins and pegmatites. In this study, high-purity quartz was prepared by purifying quartz conglomerate from Jimunai, Altay, Xinjiang. The method combined high-temperature roasting, water quenching, and ultrasonic-assisted acid leaching. The effects of process parameters on purification efficiency were systematically investigated with the aid of XRD, SEM-EDS, and ICP-OES quantitative element detection. Many cracks formed on the quartz during roasting and quenching. These cracks exposed gap-filling impurities. Gas–liquid inclusions were removed, improving acid leaching. Under optimal ultrasonic-assisted acid leaching conditions (80 °C, 4 h, 10% oxalic acid + 12% hydrochloric acid, 180 W), the Fe content decreased to 6.95 mg/kg, with an 85.6% removal rate. The total impurity content decreased to 210.43 mg/kg. The SiO2 grade increased from 99.77% to 99.98%. Compared to traditional acid leaching, ultrasonic-assisted acid leaching improved Fe removal and reduced environmental pollution.