Biocementation and calcite precipitation by intracellular extract of Sporosarcina pasteurii

Biological cementation is a new process in which urea hydrolysis bacteria or free urease enzyme decompose urea and increases the pH of the environment and chemical interactions in the presence of calcium ions to form calcite. Nowadays, nano-calcite is widely used in engineering, such as increasing the strength of soil and concrete, as well as in medicine, such as drug delivery and cancer treatment. This study aimed to investigate the laboratory conditions for producing nano-calcite particles with appropriate quality, size and purity by Sporosarcina pasteurii enzyme extract for use in medical and engineering studies. This investigation aimed to make calcite by S. pasteurii enzyme extract and optimize influential factors in calcite production. For this purpose, the bacterium S. pasteurii was cultured in nutrient broth containing urea and nickel, and upon reaching the appropriate time, the cells were separated and washed. Then, their enzyme extract was prepared by sonication, and calcite precipitation was studied in different amounts of urea, calcium chloride, enzyme and temperature. The quality of produced calcite crystals and their ratio compared to other crystals were investigated by XRD and SEM analyses. According to the results of XRD analysis, it was found that in 0.5 M urea and 0.25 M calcium chloride, the highest amount of calcite is produced with 96%, and the least side products are produced. Examining the particle size histogram in the sample containing 0.5 M urea and 0.25 M calcium chloride revealed that the range of particles were between 50 and 100 nm. The nature and type of crystals were studied by electron microscopy, and EDX analysis showed the presence of calcium, oxygen, and carbon. According to the results, it was found that by the increase of the concentrations of urea and calcium, the range of particle size became larger. Also, the percentage of calcite produced in low urea and calcium chloride concentrations is higher than those in high concentrations.