Study On The Effect Of Compound Stabilizing Agent On Ni-contaminated Soil

With the continuous development of economy and industry,environmental problems have become increasingly prominent.Heavy metals are one of the most harmful pollutants in the soil environment.After heavy metals accumulate in the soil to a certain concentration,they will cause irreversible damage to the ecological environment,hinder human production activities and endanger human health.This study studied the adsorption behavior of nickel in the soil,using stabilization remediation technology,screened different agents,and selected calcium oxide and activated carbon as composite agents to dispose of Ni-contaminated soil.The main research contents and results are as follows:The mobility of heavy metal in the soil depends on the adsorption behavior after entering the soil.Batch experiments were carried out to study the adsorption behavior of Ni in purplish soil and various influencing factors(p H,temperature and Fe³⁺concentration in background solution),and the main adsorption mechanism was revealed,laying a solid foundation for the remediation of Ni-contaminated soil.It was found that the adsorption process was commendably described by using the pseudo-second order kinetic and the Langmuir isothermal adsorption model,indicating that adsorption of Ni in purplish soil was a composite adsorption process of physical adsorption and chemical adsorption as well as a monolayer adsorption.The p H of solution was a critical factor affecting the adsorption and desorption.The maximum adsorption capacity and minimum desorption rate with the condition of p H=10 were 9.5 mg·g^-1 and 0.18%,respectively.Based on the SEM and EDS characterizations,the results that the adsorption capacity increased and desorption rate decreased were in agreement with experiment of adsorption and desorption on the condition that solution p H value was 10.The soil adsorption of Ni enhanced with an increase of temperature continuously increased,indicating that it was an endothermic reaction,while the effect on desorption was not remarkable.The presence of Fe³⁺in the solution would inhibit the adsorption of Ni,thereby promoting its desorption.By applying different addition amounts of calcium oxide,activated carbon,phosphate（trisodium phosphate,disodium hydrogen phosphate and sodium dihydrogen phosphate）,sodium silicate（modulus 2.03,3.7,4.0）and sodium sulfide was used to measure the leaching concentration of Ni after treatment.The results show that calcium oxide has a better stabilizing effect on Ni.Then carry out the compounding experiment with calcium oxide and the other four kinds of better additions.The compounding of calcium oxide and activated carbon can significantly reduce the leaching concentration of Ni,and the lowest leaching concentration is 0.10 on the 3rd day.mg/L,stable efficiency is 99.58%.The addition of calcium oxide and activated carbon and the ratio of water to soil were used to optimize the stabilization conditions of the composite agent through orthogonal experiments.The results show that the amount of calcium oxide added is the main factor affecting the leaching concentration,and the optimal conditions:4%activated carbon,1%calcium oxide,15:100（m L/g）water-soil ratio.Under the optimal conditions,the application of compound chemical to dispose of Ni-contaminated soil.The results showed that the p H value of the soil increased to 10.7 on the third day after the application of the compound agent,and gradually decreased to a near neutral range with the increase of time;the compound agent could significantly reduce the leaching concentration of Ni,and there was a problem on the third day after the treatment.The minimum value is 0.022 mg/L,and the stabilization rate remains above 99%within 45 days;the compound agent can effectively reduce the bioavailability,from 93.78%when untreated to 54.8%,reducing the Ni in the soil The harm to the human body through oral ingestion;after using the compound agent,the content of soil organic matter also increased to a certain extent,from 0.32%before disposal to 5.22%.By investigating the stabilization mechanism of the Ni-contaminated soil treated by the composite agent,SEM and BET analysis showed that activated carbon has a higher specific surface area and rich pore structure,indicating that it has a better adsorption capacity.FT-IR analysis showed that the O-H and C-O absorption peaks of the soil were weakened to varying degrees after disposal,indicating that Ni was mainly complexed with O-H and C-O.SEM-mapping results show that the activated carbon loaded on the surface of the soil particles can make the surface rough,which is conducive to the stability of Ni in the soil.The speciation analysis shows that the stabilization mechanism of the composite agent is mainly to convert the water-soluble state and weak acid extraction state of Ni into a more stable state,which is an oxidizable state and a residue state.