Physicochemical Remediation of Coal Mining Water using Carbonaceous and Geopolymeric Adsorbents to Reduce Toxicity to Enchytraeus Crypticus

Abstract

Acid mine drainage (AMD) and mine-impacted water (MIW) are major environmental liabilities, characterized by high concentrations of metals and sulfates. This study evaluated the remediation of AMD and MIW considering the individual and combined effects of chemical precipitation (CP) with NaOH and adsorption, comparing powdered activated carbon (PAC) and a modified geopolymer acid attack followed by thermal calcination (GPAT) as adsorbents for the treatment of real effluents collected in the coal mining region of Santa Catarina, Brazil. Physicochemical characterization revealed distinct structural features between the adsorbents: PAC exhibited high specific surface area and microporosity, whereas GPAT presented larger pore volume and surface silanol groups. Removal experiments demonstrated that CP was highly effective for Fe and Zn, while adsorption selectively contributed to the retention of Mn, Mg, and Cl⁻, with PAC favoring cations and GPAT showing greater affinity for anions. Ecotoxicological assays with Enchytraeus crypticus in artificial and natural soils indicated that the combined CP and adsorption treatment significantly reduced toxicity, enhancing survival and reproduction. Trend-based correlation analysis further supported that reductions in dissolved metal concentrations, particularly iron and zinc, and pH-mediated effects were key drivers of the observed ecotoxicological improvement. Interestingly, treated AMD promoted higher enchytraeid abundance in natural soil, suggesting that moderate availability of metallic micronutrients may benefit soil biota. These findings highlight the potential of integrating chemical precipitation and adsorption as a remediation strategy, combining chemical efficiency with ecological relevance and opening perspectives for the reuse of treated effluents to improve soil fertility.

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