Removal of Heavy Metals Zinc, Lead, and Cadmium by Biomineralization of Urease-Producing Bacteria Isolated from Iranian Mine Calcareous Soils

One appropriate strategy for refining heavy metals could be based on bioprecipitation by ureolytic bacteria. The study was conducted to isolate urease-producing bacteria from the contaminated soils and evaluate the potential of selected isolates in biomineralization of heavy metals.To this end, four isolates which had the greatest urease production, calcite precipitation, and endurance to the heavy metals were obtained from contaminated areas during the screening steps. These isolates along with Sporosarcina pasteurii were used to bioprecipitate zinc (Zn), lead (Pb), and cadmium (Cd) from solutions with concentrations of 100, 300, and 500 mM of these metals' ions. Amount of heavy metal precipitates formed by these bacteria were compared.Among these isolates, Stenotrophomonas rhizophila (A323) and Variovorax boronicumulans (C113) produced the highest carbonate minerals of heavy metals. S. rhizophila removed 96.25%, 71.3 %, and 63.91% of Pb, Cd, and Zn, respectively, after 72 h of incubation. Also, V. boronicumulans removed 95.93% of Pb, 73.45% of Cd, and 73.81% of Zn after having the same amount of time for incubation. S. pasteurii eliminated 98.71% of Pb, 97.15% of Cd, and 94.83% of Zn. The presence of lead, zinc, cadmium, and carbon as well as oxygen in precipitates formed from biomineralization of heavy metals was confirmed by energy dispersive spectroscopy (EDS). The S. pasteurii produced higher amounts of metal carbonates. Nevertheless, the use of selected bacteria in bioremediation of contaminated sites may be more effective due to the stability of these bacteria in high concentrations of Pb, Zn, and Cd.