| Acid mine drainage is an extraordinarily acidic and highly heavy metal ion-contaminated leachate generated from mining activities,and it has the characteristics of low p H value,high salinity,and strong heavy metal toxicity.These high concentrations of toxic heavy metals ions are non-biodegradable and prone to accumulate in the environment,resulting in various threats in nature ultimately.Therefore,finding effective treatment methods to remove the heavy metal and neutralize the acidity of the acid mine drainage will contribute to wastewater treatment and recycling.In recent years,acid mine drainage treatment has been studied through various methods such as constructed wetlands,microorganisms,neutralization,and adsorption.Notably,adsorption is an essential technique for removing heavy metals from wastewater resulted from its convenient operation,mild conditions,strong affinity and high loading capacity,compared to other approaches.Currently,there is an inevitable trend of finding high-efficiency,low-cost,and readily available adsorbents instead of traditional expensive adsorbents for the remediation of wastewater.Among industrial solid wastes,steel slag is favored in wastewater treatment due to its loose and porous surface structure,abundant functional groups,fast sedimentation velocity,and excellent solid-liquid separation.In this paper,for the low utilization efficiency of steel slag and the environmental pollution caused by acid mine wastewater with extraordinarily acidic and high heavy metal ion-contaminated,the industrial solid waste steel slag employed as a treatment agent for acid mine wastewater was proposed to investigate its removal performance and mechanism of heavy metal ions in wastewater,with the aim of water pollution control and resource utilization of solid waste.Firstly,the physicochemical properties of steel slag were analyzed,on this basis,the removal performance and mechanism of steel slag on Fe(II),a typical metal pollutant in acid mine wastewater,were studied.To further illustrate the competitive removal mechanism of different heavy metal pollutants,the removal performance and mechanism of steel slag on Fe(II),Cu(II),and Zn(II)in a multi-component system with the coexistence of heavy metal ions were also investigated.Finally,the feasibility of resource utilization of the spent slag adsorbed with heavy metals was comprehensively analyzed.The main conclusions of this work are as follows:(1)The main chemical components of steel slag are Ca O,Fe2O3,Si O2,Mg O,Mn O,and its mineral phases are mainly Ca Fe2O4,Fe2O3,Ca2Si O4,Mg O.The surface of steel slag is in a loose and disordered state and distributed in irregular blocks or cones.Steel slag is considered a mesoporous structure with wealthy active functional groups such as O-H and Si-O-Si.Besides,the p HPZCvalue of steel slag is 2.6 resulting in strong electronegativity when it is in a medium with p H>2.6.Steel slag also has a high alkalinity release ability in an aqueous solution.In the toxicity leaching experiment,the concentration of toxic heavy metal ions leached from steel slag all met the leaching toxicity identification standards.It has no secondary pollution with friendly environmental safety when applied to wastewater treatment.(2)In the single-component system,the optimum process conditions for the experiment were the steel slag particle size of 150-300?m,the initial acidity of wastewater p H 3,the steel slag dosage of 10 g/L,and the initial Fe(II)concentration of 500 mg/L.The pseudo-second-order model and Freundlich isotherm model well described the adsorption behavior of steel slag,implying that the adsorption of Fe(II)by steel slag was mainly multilayer chemisorption.The thermodynamic study illustrated that the adsorption process was endothermic and spontaneous.Mechanism study showed that the entire removal process of Fe(II)by steel slag was completed by electrostatic adsorption,chemical precipitation,and surface complexation in cooperation.Although the competitive adsorption between the coexisting metal ions in an actual system,the steel slag still had good practical application feasibility,and its Fe removal efficiency was 73.25%.(3)In the multi-component system,the optimum process conditions for the experiment were the steel slag particle size of 150-300?m,the initial acidity of wastewater p H 3,the steel slag dosage of 5 g/L,and the initial heavy metal ion concentration of 500mg/L.The adsorption kinetic models of Fe(II),Cu(II),and Zn(II)followed pseudo-second-order kinetics and were controlled by the rate-limiting step of chemisorption.Besides,the adsorption of Fe(II)by steel slag conformed to the Freundlich model,while the adsorption of Cu(II)and Zn(II)followed to the Langmuir model,in which the maximum adsorption amounts of Cu(II)and Zn(II)were 170.69 and 155.98 mg/g.Furthermore,there existed competitive adsorption among Fe(II),Cu(II),and Zn(II)coexisting in a multi-component system,and the adsorption priority was Fe(II)>Cu(II)>Zn(II).The removal mechanism of Fe(II),Cu(II),and Zn(II)in acid mine wastewater by steel slag was completed by electrostatic attraction,chemical precipitation,and surface complexation.(4)After the calcined and solidifying of the spent-slag,which adsorbed heavy metal ion,the leached heavy metal ion concentrations in water and simulated acid rain were all within the detection limit of the emission standard of“identification standards for hazardous wastes-identification for extraction toxicity”and“discharge standard of water pollutants for iron and steel industry”.It is feasible to employ the spent slag as a cement additive for preparing steel slag cement. |
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