Preparation Of Solid-waste-based Calcium Silicate Hydrate And Its Removal Performance Of Heavy Metals

Heavy metal wastewater not only causes serious pollution to our ecological environment,but also threatens human health.Therefore,it is urgent to control the pollution of heavy metal wastewater.Compared with the traditional treatment method,the adsorption process is simple,easy to operate and low in cost.It is a kind of heavy metal wastewater treatment method with good application value.Therefore,it is of great practical significance to develop new inexpensive and efficient adsorption materials for heavy metal wastewater treatment.Driven by the concept of"treating waste with waste",the research and application of new solid waste based materials has gradually become one of the important directions of adsorption technology development.In this study,solid-waste-based calcium silicate hydrate（CSH）was prepared from calcium carbide slag and the residue after aluminum extraction from fly ash by acid melting method（acid slag）.The adsorption properties and mechanism of the materials for heavy metals were studied,and the properties of the adsorption materials after treatment and the solidification/stabilization of heavy metals were discussed.In order to solve the problems of difficult recovery and easy loss of powder materials,the preparation of sodium alginate embedding of hydrated calcium silicate gel ball（SA/CSH）,investigated its removal performance together with mechanism of heavy metal ions.The specific contents were as follows:（1）CSH was prepared from acid slag and calcium carbide slag by hydrothermal synthesis,which was used to remove typical heavy metal ions such as Cu²⁺,Zn²⁺and Ni²⁺.The effects of pH value,dosage of CSH and adsorption time on the adsorption of Cu²⁺,Zn²⁺and Ni²⁺by CSH were studied by static adsorption experiments.The thermodynamics and kinetics of the adsorption process were analyzed.Combined with the characterization test data,the mechanism of heavy metal removal by CSH was discussed.The experimental results show that the optimal pH for CSH adsorption of Cu²⁺,Zn²⁺and Ni²⁺is 5.5,6 and 6,respectively.When the initial concentration of Cu²⁺,Zn²⁺and Ni²⁺is 100mg/L,the dosage of adsorbent is 20mg,and the reaction time is 120min,the adsorption capacities of Cu²⁺,Zn²⁺and Ni²⁺by CSH are 371.66,221.84 and 213.74mg/g,respectively.The isothermal adsorption process conforms to Langmuir model and belongs to monolayer adsorption.The adsorption kinetics of Cu²⁺,Zn²⁺and Ni²⁺by CSH is spontaneous and endothermic reaction,and the adsorption mechanism is mainly surface complexation and ion exchange.（2）Using sodium alginate（SA）and CSH as raw materials,SA/CSH materials were synthesized by embedding method for removing Cu²⁺,Zn²⁺and Ni²⁺from wastewater.The effects of doping ratio of raw materials,reaction pH value,SA/CSH dosage and adsorption time on Cu²⁺,Zn²⁺and Ni²⁺adsorption by SA/CSH were studied by static adsorption experiments.The isothermal adsorption and kinetic analysis of the adsorption process were carried out.The synergistic removal performance and mechanism of SA and CSH were discussed by characterization test.The results showed that the optimum pH for Cu²⁺,Zn²⁺and Ni²⁺adsorption by SA/CSH was 5.5,6 and 6,respectively.When the initial concentration of Cu²⁺,Zn²⁺and Ni²⁺was 100mg/L,the dosage of adsorbents was 50mg,and the adsorption time was 600min,the adsorption capacities of Cu²⁺,Zn²⁺and Ni²⁺by SA/CSH were145.61,108.35 and 97.33mg/g,respectively.The isothermal adsorption process conforms to Langmuir model and belongs to monolayer adsorption.The adsorption kinetics was consistent with the Ho quasi-second-order reaction kinetics model.The adsorption process was mainly chemisorption,and SA and CSH played a synergistic role.The adsorption mechanism is mainly chemical adsorption and ion exchange.In addition,EDTA disodium was used for desorption,calcium chloride solution was used to supplement calcium source,and SA/CSH adsorbent was used for three times,the removal rate decreased by 24%,showing good reuse performance.（3）The geopolymers were prepared from adsorbed Cu²⁺,Zn²⁺CSH and cement.The influence of different material mixing ratio on the compressive strength and leaching concentration of solidified body was studied.As the amount of cement increases,Compressive strength of geopolymer and pH value of leaching solution are also increasing,Cu²⁺,Zn²⁺leaching concentration decreased;Under two different leaching methods,The leaching concentration meets the HJ/T 300》HJ/T 299（HJ/T300 is the scene of simulated solidified body entering domestic waste landfill,HJ/T 299is the scene of simulated solid body entering industrial solid waste landfill by acid rain scour）.And when the cement and Cu-CSH doping ratio is 3:1,At a cement to Zn-CSH doping ratio of 4:1,The compressive strength and leaching concentration of geopolymer can reach the standard of safe landfill.There are 49 figures,23 tables and 119 references in this paper.