WSO–SVM-Based Optimization of Low-Carbon Composite Flocculant and Its Microstructural Mechanism for Engineering Waste Slurry Dewatering

To mitigate land occupation and environmental contamination from stockpiled engineering waste slurries (EWS) in coastal areas —while advancing low-carbon and circular economy goals— novel composite flocculant (FCC) was developed and optimized via the WSO–SVM hybrid algorithm to enhance EDS dewatering efficiency. Its mechanism was systematically elucidated using settling column tests, zeta potential measurements, and multi-scale microscopic characterizations (XRD, XRF, SEM, EDS, MIP), complemented by sensitivity analysis of water type, temperature, and soil texture on flocculation-sedimentation behavior. Settling tests confirmed FCC—formulated with calcium carbide residue (CCR, an industrial by-product) and cationic polyacrylamide (CPAM)—exhibits an optimal mass ratio of 0.149:0.051 via WSO–SVM optimization. Benefiting from synergistic electrostatic neutralization and adsorption bridging, FCC reduces the absolute zeta potential of EWS more effectively than single-component (CCR/CPAM) or untreated EWS. No new mineral phases form, but FCC enriches atomic concentrations of C, O, Ca, Al, and Fe, loosens EWS microstructure, and facilitates formation of coarser particles and pores. Dewatering efficiency follows deionized water > tap water > seawater (inhibited by high ionic content), with elevated temperature enhancing performance via improved molecular mobility. For EWS, sedimentation velocity, dewatering rate, and post-flocculation moisture content are strongly correlated with median particle size, providing guidance for engineering application.