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Resource utilization of gangue solid waste has become an essential research direction for green development. This study prepared a novel gangue based geopolymer adsorbent (GPA) for the removal of Cd(II) from wastewater using pretreatment gangue (PG) as the main raw material. The ANOVA indicated that the obtained quadratic model of fitness function (R2 > 0.99, P-value <0.0001) was significant and adequate, and the contribution of the three preparation conditions to the removal of Cd(II) was: calcination temperature > Na 2 CO 3 :PG ratio > water-glass solid content. The hybrid response surface method and gray wolf optimization (RSM-GWO) algorithm were adopted to acquire the optimum conditions: Na 2 CO 3 :PG ratio = 1.05, calcination temperature of 701 °C, solid content of water glass of 22.42%, and the removal efficiency of Cd(II) by GPA obtained under the optimized conditions (GPAC) was 97.84%. Adsorption kinetics, adsorption isotherms and characterization by XRD, FTIR, Zeta potential, FSEM-EDS and BET were utilized to investigate the adsorption mechanism of GPAC on Cd(II). The results showed that the adsorption of Cd(II) from GPAC was consistent with the pseudo-second-order model (R2 = 0.9936) and the Langmuir model (R2 = 0.9988), the adsorption was a monolayer adsorption process and the computed maximum Cd(II) adsorption (50.76 mg g−1) was approximate to experimental results (51.47 mg g−1). Moreover, the surface morphology of GPAC was rough and porous with a specific surface area (SSA) of 18.54 m2 g−1, which provided abundant active sites, and the internal kaolinite was destroyed to produce a zeolite-like structure where surface complexation and ion exchange with Cd(II) through hydroxyl (-OH) and oxygen-containing groups (-SiOH and -AlOH) were the main adsorption mechanisms. Thus, GPAC is a lucrative adsorbent material for effective Cd(II) wastewater treatment, complying with the "high value-added" usage of solid wastes and "waste to cure poison" green sustainable development direction. [Display omitted] • Preparation of gangue-based geopolymer adsorbents for the removal of Cd(II) from wastewater. • The optimal preparation conditions of adsorbents were obtained using the RSM-GWO algorithm. • The adsorption of Cd(II) by this material conformed to PSO model and Langmuir model with maximum adsorption rate of 97.84%. • The adsorption mechanism of Cd(II) from this material was mainly chemisorption accompanied by physical adsorption. [ABSTRACT FROM AUTHOR]

Fly ash cement is used to solidify marine clay to prepare marine-clay-based cemented paste backfill (MCCPB) to fill the underground goaf of mines, which not only utilizes solid waste such as fly ash and marine clay, but also controls surface subsidence and protects the environment. To simulate the complex underground mine water environment of the filling body, a dry-wet cycle aquatic environment test under different material ratios and curing ages was designed. The water absorption and unconfined compression strength (UCS) of MCCPB with curing ages of 7 and 28 days under the action of 0, 1, 3, and 7 dry-wet cycles were investigated. The results indicate as the number of dry-wet cycles increases, the surface of MCCPB becomes significantly rougher, and the water content and the solid mass decrease accordingly. Different ratios and curing ages of MCCPB in dry-wet cycles of the UCS tend first to increase, then decrease. Meanwhile, the stress-strain curve of the specimen shows that the trend in the elastic modulus is consistent with that of UCS (first increasing, then decreasing), and that, the minimum UCS value of the specimen still meets the early strength requirements of cemented paste backfill in coal mine geothermal utilization. On the one hand, it proves the feasibility of fly ash cement-solidified marine clay for use as cemented paste backfill in coal mines; on the other hand, it also expands the available range of cemented paste backfill materials in coal mines. [ABSTRACT FROM AUTHOR]