Direct preparation of layered magnesium hydroxide and needle-shaped aragonite through purified ash in calcium carbide industry

Abstract

The recycling and utilization of industrial solid waste exhibited significant combined environmental and economic advantages. As an industrial solid waste generated during the production of calcium carbide, the disposal of purified ash residue has long been a challenging issue in the context of solid waste resource utilization. In the present work, a novel approach was proposed to directly synthesize dispersed layered magnesium hydroxide [Mg(OH)₂] and needle-shaped aragonite from purified ash residue using wet chemical precipitation coupled with carbonation methods. This study investigated the influence of ammonia concentration and the ammonia/Mg²⁺ molar ratio on the yields and crystal forms of Mg(OH)₂, as well as the effect of ammonium bicarbonate concentration and additives on the crystal forms of aragonite. The synthesized samples were characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained results revealed that the synthesized Mg(OH)₂ exhibited a higher degree of exposed (001) crystal planes, and the I₀₀₁/I₁₀₁ results can reach 1.44. The morphology of obtained Mg(OH)₂ was lamellar with dispersed particle distribution, and the size of particles was 1–2 μm length or width and about 10 nm thickness. In addition, the synthesized aragonite has shown the shape of needles with the length–diameter ratio of 8–15. The formation and regulation of dispersed layered Mg(OH)₂ and needle-like aragonite products were closely related to the proportion and interaction between calcium and magnesium ions in the solution.