非水溶性钾矿制取碳酸钾研究:副产13X型分子筛

非水溶性钾矿通常以钾长石为主要矿物相。对其进行粉碎、摇床重选、湿法磁选和化学酸浸除铁等预处理,可制得纯度达75%~95%的钾长石粉体。以碳酸钠为助剂,在760~860 ℃的中温下钾长石发生固相分解反应,生成偏硅酸钠、偏铝酸钾(钠)前体化合物,用于水热合成13X 沸石分子筛。滤液为富含SiO2(OH)2]2-、Na+、K+的碱性溶液,通入CO2 进行酸化反应,生成SiO3·nH2O胶体沉淀,经250 ℃下煅烧即制成白炭黑。剩余滤液为NaHCO3 KHCO3 H2O三元水盐体系,再经浓缩、分离、纯化、结晶,制取碳酸钠和碳酸钾。由此,原矿中SiO2、Al2O3、K2O 3 种主要组分均可制成高值产品,可达到钾长石资源利用率接近100%、“三废”近于零排放的高效节能、清洁生产的“绿色过程”要求。本项技术实现规模化工业生产,将有利于缓解我国水溶性钾盐资源极缺的矛盾,平衡钾盐市场,提高国民经济可持续发展中钾盐资源的保证程度。

Preparation of potassium carbonate from insoluble potash ores: With 13X molecular sieve as a byproduct

Insoluble potash ores of different types from nine representative localities are characterized by potassium feldspar as major mineral phase enriched in potassium. By pretreating the ores with such a procedure as ore crushing, bed sorting, wet magnetic sorting, and iron removing by acid leaching, potassium feldspar powders with purity as high as 75% to 95% were prepared first in this research. Then, with sodium carbonate as an additive, the powders were calcinated at 760~860 ℃, leading to thermally decomposition of potassium feldspar to form a mixture of sodium metasilicate and sodium (potassium) metaluminate, from which 13X type molecular sieve was hydrothermally synthesized. The physicochemical properties of the product are as good as those of its industrial analogues. The liquors filtered from the synthesized zeolites were rich in K~+, Na~+, and \SiO_2(OH)_2\]~(2-) ions. By introducing CO_2 gas into the liquids, metasilicic acid precipitants were formed, which were further calcinated at around 250 ℃ for 2hrs to form precipitated silica. The residual liquors were then water-salt solutions in the ternary system of NaHCO_3-KHCO_3-H_2O. By evaporation, crystallization of NaHCO_3, separation from the liquids, and then evaporating the residual liquors, and crystallization of KHCO_3, both of precipitants were separated owing to much smaller solubility of the former, and at last, by calcinating the precipitants at 200 ℃ for 2hrs, both of sodium carbonate and potassium carbonate were prepared. The precipitated silica and potassium carbonate products well satisfy the China's Chemical Industrial standard HG/T 2690-95 and the China's National Standard GB 1587-2000 respectively. In such a way, the components of K_2O, Al_2O_3, and SiO_2 in potassium feldspar of the ores are all manufactured to valuable chemical products, giving rise to nearly 100% output coefficient of the potassium feldspar resources, close to zero discharge of solid wastes, wastewaters, and exhaust gases. The technique is a “green process”, characterized by energy conservation, high efficiency, and clean production. It is therefore feasible to be industrialized both in economic benefits and in environmental kindness.