Preparation of metallic arsenic from calcium arsenate by carbon thermal roasting reduction

Given the widespread application of the lime precipitation process for arsenic removal in the smelting of arsenic-containing minerals, the resourcefulness of calcium arsenate use has received increasing attention. In general, more types of arsenate have different high-temperature characteristics, and the slag type is complicated under mixed reduction roasting and difficult to recover. Additionally, arsenate in the form of calcium arsenate is a more common and inexpensive product in the metallurgical process. Because whether it is arsenic-containing wastewater, arsenic slag, arsenate, and so on, the material can be separated from the system by inexpensive lime precipitation or calcification transformation in simple metallurgical equipment to generate calcium arsenate. Therefore, this paper was devoted to preparing commercially valuable metallic monomers of arsenic by carbon thermal roasting reduction of calcium arsenate and to starting scientific research to advance the harmless treatment of arsenic hazardous waste to arsenic resource recovery and use. Among them, thermogravimetric analysis shows that the mass loss of calcium arsenate mixed with carbon powder pyrolysis is divided into 3 stages: stages 1 and 2 are water loss processes, and stage 3 involves the carbon reduction of calcium arsenate to generate CaO and arsenic vapor. It is found that the stage III reaction mechanism could be explained using the phase boundary reaction kinetic model. The experimental results of single-factor conditions show that the arsenic volatilization rate reaches 99.94% at a constant temperature of 1000 °C for 60 min and a carbon allotment factor of 1.4. The characterization of the relevant products in the reaction system by X-ray diffractometer (XRD) and scanning electron microscope energy spectrometer (SEM‒EDS) show that the arsenic product is mainly flaked metallic arsenic and amorphous powdered arsenicunder better conditions, and the roasted residue is CaO.