Comparison between microbiologically-induced calcium carbonate precipitation and magnesium carbonate precipitation

The magnesium carbonate has a cementing feature like calcium carbonate, and the strength of magnetite ore is much higher than that of calcium ore, so it is important to study the solidification technology of magnesium carbonate. The absorbance and urease activity of Sporosarcina pasteurii are measured in the cultural process, and the unit urease activity is calculated. The influences of various factors on the urease activity are studied. Some comparison tests on the precipitation efficiency between calcium carbonate and magnesium carbonate are conducted as well as the magnesium precipitation efficiency with various urea additions. The solidification tests on the calcium carbonate and magnesium carbonate are comparatively studied. The results show that during 48 h-culture period, the absorbance and urease activity curve both increase gradually and boom, then slow down and tend to be stable. The unit urease activity increases to the peak and then decreases. The increase of the urea concentration and magnesium ion can enhance the urease activity. The concentration of sodium chloride and acetate has little effect on it, and that of calcium ion has a significant inhibitory effect. Under the same condition, the yield of magnesium carbonate is significantly smaller than that of calcium carbonate. By adding urea to medium, the precipitation significantly increases. The higher the urea concentration, the more the magnesium carbonate gets. The sample with adding urea is solidified to own certain strength in the case of magnesium carbonate precipitation. Therefore, this method can solve the problem of insufficient magnesium precipitation and establish the foundation for the curing tests on magnesium carbonate in future.