Comprehensive use of dolomite-talc ore to prepare talc, nano-MgO and lightweight CaCO_3 using an acid leaching method

摘要

The talc powder associated with dolomite, from Luonan county, Shaanxi province, China, was leached with 2.25 mol hydrochloric acid (37%) to obtain MgCl_2-CaCl_2 solution and purified talc powder. The iron cations in the solution were removed by adding 9% sodium hypochlorite as an oxidant, and adjusting the solution pH to 7. Magnesium hydroxide was obtained after ammoniation of the solution using 26% ammonia until pH above 12. Magnesium oxide nanopartides were prepared by calcining the magnesium hydroxide at 800 ℃ for 4 h. Then, CO_2 gas, at concentrations of either 40% or 99.9%, was bubbled through the CaCl_2-NH_4Cl solution, to form aragonite or vaterite, respectively. This work mainly investigates the effect of molar volume of the hydrochloric acid on dolomite solution, the effect of pH on the Mg~(2+) precipitation yield, the effect of calcination temperature on the average grain size and morphology of the MgO particles, and the effect of CO_2 gas concentrations on the calcium carbonate crystal polymorphs. Scanning electron microscopy, X-ray diffraction and chemical analysis methods were used to characterize the products. The magnesium oxide nanoballs formed, with average particle size of 80-100 nm and purity of 99.14%, can be used in catalysis, as refractory materials, and in a range of other applications. The purities of both aragonite and vaterite were above 98%, and both products gave whiteness values over 96%. The technique presented in this work, which features low energy consumption and high use ratio, is a potential environmentally friendly way for clean processing of low-grade dolomite-talc ores.