Simultaneous removal of iron and sulfate from biodesulfurization solutions of a coking coal by jarosite precipitation

Abstract

Precipitation of iron- and sulfate-bearing prohibitive layers on the surface of coal particles during heap biodesulfurization is a problematic issue due to the decreasing of biodepyritization rate, causing permeability problems in bioheaps, and reducing the caking properties of coking coals. In this regard, the biodesulfurization of Parvadeh high-pyrite coking coal (Tabas, Iran) was conducted using a mixed culture of iron-and sulfur-oxidizing microorganisms and the ferric level of the bioleaching solution was controlled by jarosite precipitation. The main and interaction effects of some critical parameters including temperature, retention time, the molar ratio of ammonia to iron (MR Ammonia: Iron) and seed addition on the removal of iron from the biodesulfurization solution was investigated by jarosite precipitation using a response surface methodology (RSM). The results were evaluated by the analysis of variance (ANOVA). It was found that 98.4 % iron removal and 62.1 % sulfate removal was achieved at the temperature of 95 °C, the retention time of 2.5 h, the MRAmmonia:Iron of 0.8 and seed addition of 40 g/L. Temperature had the most effect of iron removal efficiency. The precipitates were analyzed by SEM/EDS and XRD analyses. A developed flowsheet was proposed to treat the biodesulfurization solution of coals in bioheaps.