| With the rapid development of industry,the high concentration of free metal ion in wastewater is easy to be treatmed,while the low concentration complexed metal removal is relatively hard.However,whether the complex metal can be removed effectively is the key to the safe discharge of wastewater.Chemical method is widely used in metal wastewater treatment for its rapid response,high treatment efficiency and simple operation.The chelation precipitation method is one of chemical method,of which the DTC(dithiocarbamate)has strong ability to chelate heavy metal forming metal chelate,so the chelation precipitation method efficiently remove metal pollutants from wastewater.Therefore,the DTC heavy metal capture agent is used to remove complex metals is a more promising technology.In this paper,the DTC used for trace concentration metal complex(EDTA-Cu/EDTA-Ni/TA-Ni)treatment is studied.The effect of influence factors on EDTA-Cu/EDTA-Ni removal rate treated by DDTC(sodium diethyldithiocarbamatre)was investigated.The optimum treatment conditions were determined,and the treatment results were verified by the actual complex metal wastewater.The removal mechanism was deduced.Then under the optimum technological conditions,we explored the rule of the DTC with different alkyl on the removal rate of EDTA-Ni/EDTA-Cu.The rule of the chelating ability of DTC with the same metal and the rule of the chelating ability of the same DTC agent with different metals were deduced.Moreover,a kind of heavy metal chelating resin with magnetic was developed.The adsorption efficiency of EDTA-Cu/TA-Ni(tartrate complex)by magnetic DTC chelating resin was investigated.The adsorption kinetics and isothermal adsorption characteristics were inferred.The mechanism of adsorption revealed.Thiourea-nitrate solution was used for desorption and regeneration of the magnetic DTC chelating resin,and the performance of repeated use was investigated.First of all,the effect of pH,DDTC dosage,reaction time and PAC dosage on the efficiency of EDTA-Cu/EDTA-Ni treated by DDTC were investigated,and the optimum process route was obtained:the initial concentration of Cu was 11.42mg/L,the initial concentration of Ni was 6.41mg/L,pH was 7,the dosage of DDTC was nDDTC/nNi=4mol,the reaction time was 15min,PAC 100mg/L,the reaction time was 2min,PAM 2.5mg/L,the reaction time was 2min.After treatment,the residual concentration of Ni was 1.08mg/L,the removal rate was 83.15%,the residual concentration of Cu was 0.16mg/L,the removal rate was up to 98.66%.Under the optimum technological process,three different types of Ni/Cu complex wastewater were tested to ensure removal efficiency.The results showed that Cu concentration of effluent meets the specific discharge limits of water pollutants of Pearl River Delta region of the Discharge Standard of Water Pollutants for Electroplating(DB44/1597-2015)(Ni<0.1mg/L,Cu<0.3mg/L).The Ni concentration of some types of complex wastewater can meet this requirement.According to the UV spectrum analysis,infrared spectrum analysis and elemental analysis,the chelating process of DDTC chelating agent with metal was deduced,and reaction equation and product structure were obtained.Sulfur atom of-SH group of DDTC captures the metal M of EDTA-M,forming a coordination compound with a quadrilateral stable structure.Secondly,the DTC with different straight chain alkyl were selected as SDDC(sodium dimethyl dithiocarbamate),DDTC and SBuD(sodium dibutyl dithiocarbamate).The removal efficiency of EDTA-Ni/EDTA-Cu treated by three kinds was investigated.In this paper,the rules of metal removal were observated in three different systems(pure complex metal solution,coexisting metal solution,mixed complexing metal solution).The results showed that the EDTA-Ni removal rate is proportional to the number of carbon atoms of straight chain alkyl of the DTC.But the DTC with less number of carbon atoms of straight chain alkyl can completely remove EDTA-Cu,there is no significance to increase the number of carbon atoms of alkyl to enhance the removal rate of EDTA-Cu.The rule exists in all three systems.The results of elemental analysis and scanning electron microscopy analysis showed that with the increase of the number of carbon atoms,the chelating reaction between the DTC agent and Ni happened easily and the closer the structure of chelate product was producted.The analysis of the electronic configuration of metals,the chelating ability rules of DTC with metals was obtained:Cr2+<Fe2+<Cr6+<Fe3+<Ni2+<Cu2+,Cu2+>Zn2+.The result of infrared spectrum analysis showed that the main function group of DTC chelating agent chelates with metal is-SH.And the reaction equation and the structure of product are obtained.Although the alkyls are different,the mechanism of the removal of metals by DTC is similar.Sulfur atom of-SH group of DDTC captures metal M of EDTA-M,and tends to bond to produce insoluble chelate products.Thirdly,the TEPA and carbon disulfide were used to prepare dithiocarbamate group,and then under the ethanol dispersant,dichloroethane was used as chain initiator for dithiocarbamate group monomer polymerization reaction.The polymer is produced while the Fe3O4 material modified by oleic acid is wrapped inside.A kind of magnetic mercapto amine resin(magnetic DTC chelating resin for short)was successfully synthesized.The results of infrared spectrum analysis,elemental analysis,SEM analysis,energy spectrum analysis and hysteresis loop analysis showed that the magnetic DTC chelating resin was a S=C-S bidentate ligand with a saturation magnetization of 6.84emu/g and particle size of 170.27nm.The adsorption performance of the resin for TA-Ni and EDTA-Cu were studied.After the investigating of pH,resin dosage,reaction time and the magnetic separation time,the optimum adsorption parameters of Cu/Ni were abtained.And after treatment,Cu decreased from 16.00mg/L to 0.13mg/L,and Ni decreased from 16mg/L to 0.071mg/L.Thiourea-nitric acid solution was used for desorption and regeneration for used resin.The desorption rate of used resin adsorbing Cu was about 82%,the desorption rate of used resin adsorbing Ni was about 60%.After desorption and regeneration,the resin was recycled and reused.The used resin adsorbing Cu was reused and Cu removal rate was above 75%.Fourthly,according to the pseudo second order model,the kinetic equations of magnetic DTC chelating resin adsorbing EDTA-Cu/TA-Ni were inferred.The correlation coefficient R2 showed that the sorption kinetics equations fit the pseudo second order model.According to the Freundlich isothermal adsorption model,the adsorption isotherm curves of magnetic DTC chelating resin adsorbing EDTA-Cu/TA-Ni were inferred.The correlation coefficient R2 showed that the adsorption isotherm curves fit the Freundlich model.The infrared spectrum analysis and hysteresis loop analysis showed that sulfur atom of the magnetic DTC chelating resin has coordinated with Cue+/Ni2+ of EDTA-Cu/TA-Ni to form stable complexes which were attached to the surface of the resin resulting in the decrease of magnetization of resin after reaction.The elemental analysis showed that the coordination ratio between S and M2+ in actual chelating adsorption process was larger than the theoretical ratio.That is because the effective coordination sites were relatively few on the magnetic DTC chelating resin. |
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