Synthesis Of Capture Agent TDDP And Application In Heavy Metal Ion Removal From Water

The pollution of heavy metal is an important problem of environmental protection today,and the emission requirements about heavy metal in industry wastewater is more stricter.Dithiocarbamates?DTCs?is one of research hotspots about heavy metal chelating reagents,due to its strong chelating ability to multiple heavy metal ions.At present,micromolecule DTC heavy metal capture agents are mostly two base coordination sites.The paper aims to synthesize an organic sulfur heavy metal capture agent containing mult-dithiocarbamate coordination groups,and it is used for removing heavy metal ions from acid wastewater.In this work,a heavy metal chelating reagent of N,N,N,N-tetra?dithiocarboxyl?dipiperazinewassynthesizedbytwo-stepsusing ethylenediamine,glyoxal and carbon disulfide as raw materials,which is named TDDP.The first step is to prepare dipiperazine by ethylenediamine and glyoxa,then using dipiperazine and carbon disulfide to synthesize TDDP in mixed alcohol-water solvent.The products were characterized by IR,UV and elemental analysis.The influencing factors of the second step synthesis were investigated.And the best synthesis conditions were obtained through the analysis of the amount of reactant,the ratio of solvent and reaction time and temperature.The prepared TDDP was used to treat wastewater containing single heavy metal ions?Cu,Pb,Zn,Cd?and mixed solution of heavy metal ions.Based on the removal rate of heavy metal ions under different conditions,the heavy metal capture performance of TDDP was investigated,and the best conditions for the treatment of low concentration wastewater were also analyzed.The experimental results show that:?1?Optimal synthesis conditions of TDDP as follows:The molar ratio of reactants was n?dipiperazine?:n?CS₂?:n?NaOH?=1:8:1;The volume ratio of purified water and alcohol was V?alcohol?:V?water?=2:1;The reaction temperature was 30?,and the reaction time was 3hours.And the yield of TDDP is 73%.The structure of TDDP were characterized by UV,IR and elemental analysis,which indicating that the products contained dithicarbamate groups,and the molecule formula was C₁₀N₄S₈H₁₄.?2?Removal effect of heavy metal capture agent TDDP on single ions Cu²⁺?Pb²⁺?Cd²⁺?Zn²⁺:for 10mg/L low concentration of heavy metal solutions,The best dosage of Cu²⁺,Pb²⁺,Cd²⁺and Zn²⁺were 0.5,0.5,1.5,0.4 times of their molar weight respectively,and the remaining concentration is up to the national emission standard.The applicable range of pH values is 4¹1,adding 1mL1%PAM flocculant and reacting 5 minutes.?3?When TDDP dosage is 1 times stoichiometric,it can remove multiple heavy metal ions together,so that the residual concentration reaches the national emission standard.Compared with the single ion treatment,the removal rate is improved.The reason is that chelation of TDDP and Cu²⁺will lead to the enrichment and co precipitation of other heavy metal ions.It has good removal effect under acidic condition of pH=4⁶,but it is not effective in strong acid environment.In addition,it can also promote the removal of coexisting heavy metal ions by TDDP in alkaline medium.The selectivity order of TDDP removing heavy metal ions is Cu²⁺>Pb²⁺>Cd²⁺>Zn²⁺.?4?The precipitate of metal ions and TDDP has good stability,low leaching rate under weak acid and weak base conditions,and it can exist in a long term and is not easy to cause two times of pollution.