[Impact of Tailings Residue on the Quality and Carbon Transformation in Pig Manure Composting]

The appropriate use of external additives can reduce greenhouse gas emissions from livestock manure composting and improve compost quality. Using basalt and diorite tailings as subjects, this study investigates the effects of these tailings residues on compost quality, carbon transformation, and retention, as well as CO₂ and CH₄ emissions during the composting process. The results showed that, similar to the control compost, the compost products with 10% basalt and diorite tailings residue treatments met the NY/T 525-2021 organic fertilizer standards in terms of heap temperature, pH, organic matter, and total nutrient content. This addition also reduced moisture, improved the seed germination index, and supported organic matter and total nutrient （N, P, and K） accumulation. Notably, in the basalt treatment, organic matter loss rate decreased from 15.6% to 2.6% compared to that in the control, and total nutrient accumulation increased from 101% to 114.6%. The addition of basalt tailings aided in carbon stabilization within pig manure compost. Compared to that in the control treatment, the total organic carbon loss rate in the basalt tailings residue treatment decreased from 15.6% to 2.9%. Non-soluble organic carbon accumulated, CO₂ and CH₄ cumulative emissions from composting were reduced by 23.5% and 24.4%, respectively, and the humification coefficient of the compost product increased by 56.3%. Nuclear magnetic resonance carbon spectroscopy further indicated that the addition of tailings residues promoted the decomposition of lignocellulosic components in the pig manure heap, facilitating their transformation into more stable aromatic carbon. The study provides important theoretical and technical support for the efficient, low-carbon, and synergistic recycling of tailings and livestock manure.