Comprehensive use of dolomite-talc ore to prepare talc, nano-MgO and lightweight CaCO3 using an acid leaching method

The talc powder associated with dolomite, from Luonan county, Shaanxi province, China, was leached with 2.25mol hydrochloric acid (37%) to obtain MgCl2–CaCl2 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 nanoparticles were prepared by calcining the magnesium hydroxide at 800°C for 4h. Then, CO2 gas, at concentrations of either 40% or 99.9%, was bubbled through the CaCl2–NH4Cl 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 Mg2+ precipitation yield, the effect of calcination temperature on the average grain size and morphology of the MgO particles, and the effect of CO2 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 80–100nm 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. [Display omitted] •A new green and environmentally friendly way of dolomite processing was introduced.•Purified talc can be obtained from dolomite-talc ore by HCl leaching.•Magnesium hydroxide is synthesized by ammoniating the CaCl2-MgCl2 solution.•Nano-magnesium oxide can be obtained by calcining the magnesium hydroxide at 800°C.•Aragonite and vaterite were obtained at different CO2 concentrations.