Research on sulphur conversion and acid balance from marmatite in pressure acid leaching

In this paper, the kinetics of oxygen pressure acid leaching of marmatite was studied in the low-temperature region (383–413 K). The effects of agitation rate, particle size, temperature, H2SO4 concentration and oxygen partial pressure on the conversion of sulphur (S2− → S0) were investigated. The results showed that the conversion ratio increased with increasing agitation rate, temperature and oxygen partial pressure, and with decreasing particle size and H2SO4 concentration. Moreover, the results demonstrated that sulphur conversion was controlled by an interfacial chemical reaction, with an apparent activation energy of 51.17 kJ mol−1. The calculated reaction orders of sulphuric acid and oxygen were 0.48 and 1.01, respectively. The leaching reaction followed an unreacted shrinking core model. A model kinetic equation was established for sulphur conversion. Orthogonal experiments regarding the acid balance () of the oxygen pressure leaching residue were carried out. Variance analysis showed that temperature had the largest influence on this, so the effect of the temperature region (383–443 K) on acid balance was further investigated. When the temperature exceeded 443 K, the increase in the sulphur oxidation ratio was too large, which tended to increase the acidity of the system.