Copper slag assisted coke reduction of phosphogypsum for sulphur dioxide preparation

Abstract

The reduction of phosphogypsum (PG) to lime slag and SO2 using coke can effectively alleviate the environmental problems caused by PG. However, the PG decomposition temperature remains high and the product yield remains poor. By adding additives, the decomposition temperature can be further reduced and PG decomposition rate and product yield can be improved. However, the use of current additives such as Fe2O3 and SiO2 brings the problem of increasing economic cost. Therefore, it is proposed to use solid waste copper slag (CS) as a new additive to reduce PG to prepare SO2, which can reduce the cost and meet the environmental benefits at the same time. The effects of proportion, temperature and thermostatic time on PG decomposition are investigated by experimental and kinetic analysis combined with FactSage thermodynamic calculations to optimize the roasting conditions. Finally, the reaction mechanism is proposed. It is found that adding CS to the coke and PG system can increase the rate of PG decomposition and SO2 yield while lowering the PG decomposition temperature. For example, when the CS/PG mass ratio increases from 0 to 1, PG decomposition rate increases from 83.38% to 99.35%, SO2 yield increases from 78.62% to 96.81%, and PG decomposition temperature decreases from 992.4 °C to 949.6 °C. The optimal reaction parameters are CS/PG mass ratio of 1, Coke/PG mass ratio of 0.06 at 1100 °C for 20 min with 99.35% PG decomposition rate and 96.81% SO2 yield. The process proceeds according to the following reactions: 2CaSO4+ 0.7C + 0.8Fe2SiO4→0.8Ca2SiO4+ 0.2Ca2Fe2O5+ 0.4Fe3O4+ 2SO2+ 0.7CO2 Finally, a process for decomposing PG with coke and CS is proposed.