Contribution of ferric-iron precipitate to the kinetics of microbial ferrous-iron oxidation by Leptospirillum ferriphillum in a packed column

摘要

Ferric-iron generation from microbial ferrous-iron oxidation sub-process is critical to bioleaching of sulphide minerals. The availability of the ferriciron reagent in solution is also important to the lifespan of a typical bioleach heap system, as ferric-iron precipitate may reduce heap permeability if allowed to accumulate within a heap bed. In this study microbial ferrous-iron oxidation kinetics was investigated in packed column reactor which was operated in a manner that represents solution flow dynamics in a typical heap situation. Marble balls (15 mm in diameter) were used as reactor packing and the operating conditions of pH 1. 45 ± 0. 05 , aeration rate, 15 mlVs and temperature of 30X1 were maintained. The effect of accumulation of ferric-iron precipitation (jarosite) due to prolong period of experiment was compared to jarosite limited experiment with respect to the oxidation kinetics. The results showed that the microbial ferrous-iron oxidation rates increase linearly with ferrous-iron loading (dilution) rate for both systems. Although about 4% jarosite was obtained from the bioreactor effluent at every dilution rate investigated, most of the jarosite accumulated within the bioreactors, serving as support for microbial attachment. Ferrous-iron conversion did not follow a definite trend with dilution rate due to jarosite accumulation, it decreases and also increases with the increase of dilution rate, however, conversion greater than 90% was obtained at the highest dilution rate (0. 10 h-1) investigated. The analysis of the results using a simplified ferric-inhibition model (a modified Hansford model) and a Monod equation revealed that the maximum overall rates of microbial ferrous-iron oxidation, rmaxFe2+ , obtained from both equations are the same. However, the average value increased by 38.91% due to accumulation of jarosite, the substrate affinity constant, KFe2+ , and the apparent affinity constant, K'Fe2+ , significantly decreased with jarosite accumulation. This study shows that jarosite, though known to be undesirable in bioleach heaps may be used to heap operators' advantage if carefully managed. Current study is directed towards the management of jarosite in packed column system.