Macroscale preparation of nanosized calcium carbonate by exploiting biogas slurry synchronous metathesis encapsulation method

Abstract

The excessive biogas slurry produced by anaerobic fermentation seriously constrains the sustainable development of the biogas industry. It is significantly important to realize the resource utilization of biogas slurry. However, biogas slurry contains abundant weak electrolytes of bicarbonate (HCO₃⁻), leading to the negative influence of low conductivity, fouling, and scaling on electrodialysis for nutrient recovery. The synchronous metathesis method was first proposed to prepare humic acid-based nanosized calcium carbonate (HA-NCC) using CaCl₂, CaO, and NaOH reacted with HCO₃⁻ and HA in biogas slurry to resolve weak electrolyte problems. HA-NCC was decolored to obtain white NCC by a bleaching method and one-step burning method. The NCC whiteness reached 90.4% through a simple one-step burning method at 700 °C for 2 h, which is superior to the bleaching method. The white NCC was needle-like, rod-like, and spindle-like with preferable dispersion properties and a particle size between nanometer and micrometer. However, the particle size of white NCC was smaller compared to commercial NCC. The NCC was calcite and further confirmed the composition of CaCO₃ by XRF. The results are beneficial for the development of high-end NCC products to realize the high-value utilization of biogas slurry.