Solution pH and Jarosite Management during Ferrous Iron Biooxidation in a Novel Packed-Column Bioreactor

Abstract

Jarosite formation is undesirable in bioleaching processes as it depletes the needed ferric reagent for the oxidation of most sulfide minerals. Although it creates kinetic barriers thereby retarding the leach rates of most minerals, jarosite serves as support for the attachment of bioleaching microbes, facilitating biooxidation rate. Microbial ferrous-oxidation by mesophilic microbe was studied in a recently reported novel packed-column bioreactor with a view to investigate the potential of using solution pH to manage jarosite accumulation in the bioreactor in addition to establishing a base case data for the bioreactor. Experiments were conducted in the bioreactor packed with glass balls (15mm diameter) at constant temperature of 38.6 °C, residence time of 18 hours, airflow rate of 20 mLs-1 and pH values of 1.3, 1.5 and 1.7. The results showed that the amount of jarosite accumulation is proportional to the solution pH, and to the duration of operation of the bioreactor. Jarosite precipitation concentrations of 4.95, 5.89 and 7.08 gL-1 were obtained after 10 days of continuous operation at solution pH values of 1.3, 1.5 and 1.7 respectively, while after 15 days the precipitations concentrations increased to 5.50, 7.90, 9.98 gL-1 respectively. The results also showed that 33% and 52% precipitate reduction could be achieved by gradual decrease in the bioreactor solution pH to 1.5 and 1.3 after being continuously operated for 10 days at pH 1.7 respectively after an addition of 5 days. A maximum ferrous oxidation rate (), 6.85 mmol.L-1.h-1 and the affinity kinetic constants (,), of 0.001 and 0.006 for Hansford and Monod models respectively. Although a directly relationship exist between jarosite formation and pH, the results of this study may be relevant in bioleach heaps or at least in column bioreactors to manage/control jarosite accumulation thereby improving the leach kinetics of mineral sulfides.

Microbial Ferrous Ion Oxidation versus Ferric Ion Precipitation at Low Temperature Conditions

“…The effect of temperature on ferric precipitate was investigated at 6, 7, 8 and 10°C. The total iron concentration was determined by titration method at regular intervals after filtering solution samples with 0.45 µm membrane [9]. All the chemicals used in this study were of analytical reagents.…”

“…However, it is not clear whether ferrous ion oxidation and ferric ion precipitation are coupled, i.e occur concurrently or precipitation is preceded by the oxidation process. Although it is hypothesized that there is a treshould concnetration of ferric ion in solution that is necessary for precipitation, previous studies simply quantified ferric precipitate as a function of time [6][7][8][9]. This study investigated ferrous ion biooxidation at low temperature condition with a view to investigating ferric ion precipitation kinetics and establish whether both processes are coupled or not.…”

The Effect of Initial Solution pH on Surface Properties of Ferric Ion Precipitates Formed during Biooxidation of Ferrous Ion by <i>Leptospirillum ferriphilum</i>

“…Availability of ferric ion, (Fe 3+ ), in soluble form is one of the requirements necessary to sustain bioleaching of sulphide minerals. Due to its low solubility at pH > 2.2 [1,2], it forms various types of iron precipitates that are amorphous in nature and have high surface area, thus decreasing metal extraction efficiency by an adsorption mechanism that is not well documented. Recent studies show that significant amount of metals were recovered from treatment of jarosite from biohydrometallurgical processes [3,4].…”

“…Recent studies show that significant amount of metals were recovered from treatment of jarosite from biohydrometallurgical processes [3,4]. Moreover, even though there were several studies on ferric ion precipitate in the context of bio or hydro-metallurgy, they were limited to mineralogy, physical and chemical composition [1,2].…”