Reduction of phosphogypsum to calcium sulfide (CaS) using metallic iron in a hydrochloric acid medium

Abstract

Our study aims to decompose phosphogypsum (PG), mainly composed of CaSO 4 .2H 2 O, by reduction in an acidic medium. We evaluated the decomposition of PG by various reaction mechanisms. Sulfate ions from the acid digestion of PG are reduced to sulfide by the hydrogen gas produced in the solution by hydrochloric attack of the metal iron. The solid residues obtained have been determined and monitored by X-Ray Diffraction, Fourier-Transform Infrared spectroscopy and Ultraviolet-visible spectroscopy. The microstructure of residues was observed by scanning electron microscope (SEM). The results show that hydrogen gas formed by hydrochloric acid attack of iron reduces the sulfur from S(VI) to S(-II). CaSO 4 .2H 2 O, insoluble in water, gives a residue containing CaS, which is only sparingly soluble in water. The residue also contains anhydrite, bassanite and ferrous chloride. The monitoring of the quantities of residue obtained under varying experimental conditions (temperature, attack time, mass of iron and PG and volume of acid on PG) and volume of HCl showed that the amounts of residue obtained are less than 32% of mass. When the volume of the HCl added increases, the obtained mass of the solid residue decreases sharply. The residue stabilizes at 10% of mass when the volume of HCl added is higher than that required to attack metal iron.

Phosphogypsum-Modified Vinasse Shell Biochar as a Novel Low-Cost Material for High-Efficiency Fluoride Removal

“…EDS analysis showed that the phosphogypsum was mainly composed of Ca, S, and O. This was consistent with the fact that the main component of phosphogypsum was CaSO 4 [35]. The EDS images also showed that MVS600 contained much more Ca, S, and O than VS600, suggesting that phosphogypsum combined well with vinasse shell biochar.…”

Removal of hydrogen sulfide in the gas phase by carbide slag modified bentonite

“…In addition, the hydrolysis of calcium sulfide at low temperatures made the adsorption of H 2 S more suitable for high temperatures (eqn (20)). 35,36 Ca(OH) 2 + H 2 S → CaS + 2H 2 OCa(OH) 2 + 2H 2 S → Ca(HS) 2 + 2H 2 OCaCO 3 + H 2 S → CaS + H 2 O + CO 2 CaS + 2H 2 O + 2CO 2 → CaSO 4 ·2H 2 O + 2CCa(HS) 2 + H 2 O + CO 2 → CaCO 3 + 2H 2 SCaS + H 2 O → Ca(OH) 2 + H 2 S…”

Studying the Process of Phosphogypsum Recycling into a Calcium Sulphide-Based Luminophor

“…One of the possible applications of phosphogypsum is its use as a raw material for calcium sulfide synthesis [ 21 , 22 , 23 , 24 , 25 ]. Luminescent materials are produced based on CaS [ 26 ].…”