Selection Of Cadmium And Arsenic Adsorption Materials And In-situ Synchronous Remediation Study

Heavy metal pollution has become an increasingly pressing global environmental issue,with severe consequences for natural ecosystems.Cadmium（Cd）and arsenic（As）are internationally recognized as potentially toxic and carcinogenic elements,widely present in water and soil,accumulating in organisms through the food chain,and posing significant risks to human health.Remediation of heavy metal pollution in water and soil and reducing its environmental risk are of great importance."In-situ removal"of soil heavy metals is the fundamental solution for soil heavy metal pollution remediation.Based on this idea,this study explores the in-situ remediation effects and mechanisms of different adsorption materials on cadmium and cadmium-arsenic co-contaminated soil.The study first selects stable and efficient adsorption materials,and through constant temperature and humidity soil culture experiments and rice（Oryza sativa L）soil pot experiments,evaluates the in-situ remediation effects of typical materials and a"recyclable in-situ removal device"on soil cadmium bioavailability,morphological transformation,and cadmium pollution.Based on this,a silicate-bonded titanium-modified ultrasonic calcium-based magnetic biochar material is further modified and prepared,and its synchronous adsorption effects and mechanisms on cadmium and arsenic are explored.The main findings of the study are as follows:1.The study compared the in-situ adsorption effects of various natural materials on cadmium and finds that biochar（BC）and steel slag（SS）have strong adsorption capacity for cadmium,with maximum adsorption capacities of 16.6 mg/g and 23.3 mg/g,respectively.Both materials have strong water stability,and the optimal p H and temperature for cadmium adsorption are 5.0-7.0 and 25-35°C,respectively.Inorganic acid desorption agents can effectively dissolve heavy metals,indicating that the materials are easy to recover and reuse.2.Constant temperature and humidity soil culture experiments were used to evaluate the in-situ removal effects of BC,SS,and cation exchange resin（CER）on cadmium in contaminated soil and the influence on soil cadmium bioavailability and chemical form transformation.The results show that BC and SS can significantly reduce soil cadmium content,with total cadmium in two types of soil（brown soil and red soil）decreasing by 39.2%and 42.2%,respectively,and available cadmium decreasing by 3.5%～10.6%.3.Using CER,BC,and SS as filler materials,a recyclable device for in-situ removal of cadmium was independently designed.Rice soil pot experiments are used to study the in-situ removal effects of the device on cadmium in two types of rice soil,rice growth and development,and cadmium health risks.The results show that the use of the three devices reduces soil cadmium content by 12.6%,16.2%,and 19.8%,respectively,reduces rice cadmium accumulation by 30.6%,16.1%,and 29%,and increases rice yield by 70.3%,42.6%,and 55.4%.The use of the device also increases rice photosynthesis and relative abundance of beneficial soil microbial communities while reducing rice oxidative damage.Grey correlation analysis and human health risk index（HRI）analysis indicate that the in-situ removal device can reduce the health risk of cadmium in rice.This research provides a new solution for soil heavy metal pollution remediation.4.To address the issues of biochar’s inability to simultaneously remove cadmium and arsenic,poor physical strength,and difficulty in recovery,biochar was magnetically modified,loaded with nano-sized Ti O₂,and bonded using water-hardened silicate gel materials ordinary portland cement（OPC）to prepare a low-cost,recyclable,and highly water-stable material Silicate-Bonded Titanium-Modified ultrasonic calcium-based magnetic biochar（SCBT）.Laboratory batch studies show that SCBT can simultaneously remove aqueous cadmium and trivalent arsenic.The process of adsorption aligns with the pseudo-second-order kinetic model,Langmuir model,Freundlich model,and internal particle diffusion model.The maximum adsorption capacities of SCBT for cadmium（110.8 mg/g）and As（29.1 mg/g）are significantly higher than those of other biochar materials.The optimal p H for adsorbing both heavy metals ranges from 2 to 7,with the best p H being 6.The co-adsorption mechanism of cadmium and arsenic involves competitive and synergistic effects.The presence of co-existing cadmium increases the adsorption of arsenic by SCBT from 1.8%to 43.7%,and its synergistic effect is caused by electrostatic interactions and the formation of type-A ternary surface complexes.This research successfully combines magnetic iron oxides,Ti O₂,and OPC on the surface and internal pores of bamboo biochar,increasing its specific surface area and pore volume,and improving its surface functional groups,thus significantly enhancing the simultaneous removal effects of biochar on cadmium and arsenic.In addition,this modification method improves the physical stability of biochar,with a strength 24.5%higher than that of cement particles.Material characterization results reveal that the main adsorption mechanisms of SCBT are ion exchange,surface precipitation,chelating oxidation,and electrostatic adsorption.The aforementioned results indicate that this highly efficient and recyclable adsorbent has great application potential.