The impact of four distinct calcium sources on the microbial solidification of sand in the Kashi Desert, Xinjiang, was investigated. A wind tunnel test over a 60-day period revealed the cracking behavior of four different complex calcium nutrient solutions. By comparing the bearing capacity and the results from dry-wet cycling and freeze-thaw cycle tests, it was concluded that the sample treated with calcium gluconate exhibited superior sand fixation performance, whereas the sample treated with calcium acetate showed weaker sand fixation effects. The microstructure of the treated sand samples was analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Elemental analysis was conducted via energy dispersive spectroscopy (EDS), and functional groups were identified through Fourier transform infrared spectroscopy (FTIR). These experimental findings hold significant implications for soil remediation, pollutant removal in soil, enhancement of soil fertility, and desert soil stabilization.

Microbial induced carbonate precipitation (MICP) is gaining recognition for enhancing the mechanical properties of construction materials. This study aims to explore the potential of using phosphogypsum (PG), a solid waste mainly composed of CaSO42H(2)O, as both a sufficient calcium source for MICP based bio-cement and an aggregate for mine backfill applications. First, the interaction between MICP bacteria and the PG was assessed by monitoring pH, electrical conductivity, and Ca2 + and SO42- levels. Results indicated that bacteria maintained robust urease activity in the PG environment, leading to CO32- production. These ions, combined with the Ca2+ naturally present in PG to form CaCO3 precipitation, which acted as a binding agent for PG backfill. Further testing of the bio-cemented PG backfill showed excellent fluidity which is suitable for efficient pipeline transportation in underground mining. After a 7-day curing period, the backfill exhibited an unconfined compressive strength (UCS) of 947 kPa, meeting the standards for mining backfill applications. Additionally, the environmental impact of the bio-cemented PG backfill was notable. Unlike traditional cement-based backfills with high pH levels (>11), the leachate from the bio-cemented PG backfill maintained a neutral pH (7.16), highlighting its eco-friendly nature. This positions the bio-cemented PG backfill as a sustainable solution for the construction and mining industries.

Good bioactivity and tunable mechanical properties of akermanite (Ca2MgSi2O7), as compared to calcium phosphate materials, have garnered increasing attention as a potential bone substitute material. Typically, these Ca-Mg-Si bioceramics are synthesised using commercially available chemicals. In this study, we aimed to transform clinical dental mould waste (DMW) into an alternative calcium source used in synthesising akermanite ceramics. The DMW were initially refined involving alkaline roasting and caustic leaching, resulting in high purity Ca(OH)2 powder. This Ca(OH)2 powder was then mixed with MgO and SiO2 in stoichiometric proportion and subsequently subjected to planetary ball milling, pressed into pellets and sintered at 1200-1250 degrees C, forming the desired akermanite ceramics. Two calcium sources were investigated: Ca(OH)2 refined from DMW and chemically available CaO. Comparative analyses between Akr-Ca(OH)2 and Akr-CaO confirmed that both types of akermanite ceramics exhibited akermanite as the major phase with a minor phase of diopside. Regardless of the calcium source used, the physical and mechanical properties of the akermanite produced improved with increasing sintering temperature. However, Akr-Ca(OH)2 possess relatively lower mechanical properties than Akr-CaO. These intriguing findings underscored the potential for utilising calcium derived from DMW in producing akermanite ceramics with acceptable mechanical properties. Utilising this sustainable approach to create akermanite ceramics for bone substitutes may indirectly alleviate environmental pollution. This is because dental mould waste (DMW), which contains small amounts of chromium that can leach out and harm soil quality when discarded into landfills, is minimised. Furthermore, this innovative method shows potential for providing an affordable bone substitute option for patients in need.