[Formation of huntite by Lysinibacillus sp. GW-2 strain]

We studied the formation of carbonate minerals induced by microorganism to explore the possibility of mineral capture.

Culture experiments of carbonate precipitation were done using B4 medium with 6:1 molar ration of Mg/Ca for 50 days. The same medium without inoculation was used as the control. During the cultivation, bacterial density, precipitate quantities, pH and conductivity of the medium, calciumand magnesium concentration were determined. The morphologies of precipitated carbonates were observed using scanning electron microscopy, and mineral species of carbonate were determined by X-ray diffraction.

The main results were: (1) In the inoculation process of the Lysinibacillus sp. (GW-2 strain), we found that precipitate quantities were gradually increased with time, while precipitate was not collected in the aseptic experiments; (2) There were significant positive correlations between bacterial density and average precipitation rate (r = 0. 67, P < 0.05), precipitate quantities and pH value (r = 0.79, P < 0.05); (3) Precipitate quantities negatively correlated with conductivity, Ca2+ and Mg2+ concentration with correlation coefficients r of 0.89, 0.93, 0.98 (P < 0.001), respectively; (4) The three carbonate minerals by Lysinibacillus sp. formed according to following trend: amorphous calcium carbonate --> Huntite --> High-Mg calcite.

The main conclusions were: (1) Lysinibacillus sp. (GW-2 strain) might induce the formation of carbonate minerals precipitation; (2) The bacterial density directly affected the precipitation of carbonate minerals, whereas pH value indirectly controlled the precipitation of carbonate minerals; (3) Decreased of conductivity, calcium and magnesium concentration of the medium could indirectly indicate the occurrence of carbonate precipitate; (4) Huntite might be formed through ageing of amorphous calcium carbonate, whereas high-Mg calcite might be formed through demagnesium of the huntite.