To overcome the high cost, marine ecological risks of traditional coral sand reinforcement, and the insufficient mechanical performance of standalone Enzyme-Induced Carbonate Precipitation (EICP), this study proposes a novel soil improvement method integrating EICP with aluminum chloride hexahydrate (AlCl₃·6H₂O). The objectives are to identify optimal EICP curing parameters, evaluate AlCl₃·6H₂O’s enhancement effect, and reveal the synergistic micro-mechanism. Through aqueous solution, unconfined compressive strength, permeability, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and Scanning Electron Microscope (SEM) tests, this study systematically investigated the reaction conditions, mechanical properties, anti-seepage performance, mineral composition, and pore structure. The results demonstrate that EICP achieves the best curing effect under specific conditions: temperature of 30 °C, pH of 8, and cementing solution concentration of 1 mol/L. Under these optimal conditions, the unconfined compressive strength of EICP-solidified coral sand columns reaches 761.6 kPa, and the permeability coefficient is reduced by one order of magnitude compared to unsolidified samples. Notably, AlCl₃·6H₂O incorporation yields a significant synergistic effect, boosting the UCS to 2389.1 kPa (3.14 times standalone EICP) and further reducing permeability by 26%. Micro-mechanism analysis reveals that AlCl₃·6H₂O acts both by generating cementitious aggregates that provide nucleation sites for uniform calcite deposition and by accelerating the transformation of metastable aragonite and vaterite to stable calcite, thereby enhancing cementation stability. This study delivers a cost-effective, eco-friendly solution for coral sand reinforcement, providing practical technical support for marine engineering in environments like the South China Sea. By addressing the core limitations of conventional bio-cementation, it opens new avenues for advancing soil improvement science and applications.

Developing efficient, low-resource adsorbents from solid wastes is critical for heavy-metal wastewater treatment. Here, solid-waste-based geopolymer adsorbents were prepared from ground granulated blast-furnace slag (GGBFS) and carbide slag (CS) at a CS:GGBFS mass ratio of 15:85, with 0–30 wt% rice husk biochar (BC) as a functional modifier. The effects of pH, contact time, adsorbent dosage, and initial Cu²⁺ concentration on adsorption were evaluated. The BC-2% adsorbent achieved a maximum adsorption capacity of 208.85 mg/g at pH 4, an adsorbent dosage of 1 g/L, and an initial Cu²⁺ concentration of 300 mg/L, 48.65% higher than the BC-free control; equilibrium was reached within approximately 80 min. Low BC contents (≤5 wt%) improved adsorption capacity and initial adsorption rate, whereas excessive BC (≥10 wt%) reduced performance. Kinetic and isotherm analyses revealed that Cu²⁺ uptake followed pseudo-first-order behavior and was better described by the Langmuir and Dubinin–Radushkevich models, indicating a physically dominated process controlled by finite surface sites, pore filling, and multiple mass-transfer steps. Brunauer–Emmett–Teller (BET) and Fourier transform infrared spectroscopy (FTIR) analyses showed that low BC addition increased the specific surface area and enriched hydroxyl and amino groups, thereby improving site accessibility and surface affinity, whereas high BC contents weakened these structural and interfacial advantages. This study offers a practical route for converting industrial and agricultural wastes into low-cost Cu²⁺ adsorbents.