Selective Removal And Mechanism Of Heavy Metals And Flotation Reagents From Floatation Wastewater By Electrocatalytic Internal Micro-electrolysis

Flotation is the main form of the enrichment of nonferrous metal mineral which would produce large amount of flotation wastewater.Flotation wastewater contains lots of toxic and harmful heavy metal ions and flotation reagents.The excessive emissions will cause serious environmental pollution problems.It has greatly influence on mineral separation indexes when flotation wastewater reused directly or could not meet the standard after treatment.This is an important factor which restricts the healthy development of the non-ferrous metal industry.China is the world’s largest lead and zinc production country and flotation is the most widely applied processing method.At present,the treatment of lead-zinc flotation wastewater is difficult to achieve the purpose of zero-emission or reusing completely.Therefore,the development of a novel processing technology of low cost and short process has important significance for the healthy development of ore dressing industry nonferrous metal.Internal micro-electrolysis shows a superior performance in removal of heavy metals and degradation of organic pollutants,respectively.It will have great potential that if internal micro-electrolysis is applied in the treatment of heavy metal and flotation reagents from lead-zinc flotation wastewater.And there is no report about these related research and application.Meanwhile,internal micro-electrolysis also has some limitations,such as small providing of reaction overpotential,limiting ability of catalytic degradation,slow reaction rate,easiness of hardening and inactivation,and larger reliance on the reactivity of filler and pH,etc.According to the limitations of internal micro-electrolysis,the process of electrocatalytic iron/carbon internal micro-electrolysis(ECIME)was proposed through introducing external electric field in system of internal micro-electrolysis to electrocatalytic the reactions.And the simultaneous treatment of Pb2+,Zn2+,BX and DDA by ECIME from lead-zinc flotation wastewater was investigatedBased on these,lead-zinc flotation wastewater is subjects of the study.The most common heavy metal ions in lead-zinc flotation wastewater is Pb2+,Zn2+and the most frequently used flotation reagents for lead-zinc flotation is butyl xanthate(BX)and dianilino dithiophosphoric acid(DDA).So these four contaminants were selected as typical representation to the study.The selective removal of Pb2+,Zn2+,BX and DDA from lead-zinc flotation wastewater in ECIME system has been conducted.This study puts forward a new method of pollutants selective removal based on the characteristics of lead and zinc flotation wastewater and reused requirements.The researches have been conducted to adopt pollutants selective removal(namely,heavy metal ions which influence the effect of flotation separation and enrichment would be removed xanthate collectors which easily degraded and poor flotation selectivity would be degraded Whereas dithiophosphate collectors which has high price,refractory and well flotation selectivity would be reserved)to instead of traditional methods which always considered pollutants removal completely.Developed a novel method which is characteristics of brief process,less influence on flotation indexes when reused after treatment,and low dosage and cost of dithiophosphate collectors,so that purification wastewater can be reused completely.The primary investigation included the reaction characteristics,degradation and removal mechanisms of Pb2+,Zn2+,BX and DDA in ECIME system.And it was comparative analyzed that the variation of reaction characteristics,interaction effect and mechanism of Pb2+,Zn2+and BX,DDA in single and composite system of heavy metals and flotation reagents.Furthermore,explore the potential treatment channels of lead-zinc flotation wastewater.The main research conclusions are as follows:(1)The removal of Pb2+,Zn2+through electric reduction deposition in internal micro-electrolysis system is improved effectively by the electrocatalysis of external electric field.There was no alternative of the removal of Pb2+and Zn2+in ECIME system.The dominant removal mechanisms of Pb2+,Zn2+were electrochemical reduction and Fe-based flocculation.Results showed that Fe0/C filler could be regarded as large amount of particle electrodes due to the repolarization function of external electric field.And the corrosion rate of iron and the electrochemical reduction Pb2+ and Zn2+ were improved.The reaction active sites of ECIME system are Fe0/C filler after repolarization.The electrocatalytic reduction of Pb2+ and Zn2+is greatly influenced by the polarization of the external electric field.The cathodic polarization is beneficial to the reduction deposition,while the anode polarization shows impede effect.The effective mechanisms of the rapid removal of heavy metal ions in EIMCE system are electrocatalytic reduction and Fe-based flocculation.Relatively speaking,the electrocatalytic reduction is the dominant mechanism for the removal of Pb2+,while the removal of Zn2+is mainly based on Fe-based flocculation.(2)The degradation mechanism of BX,DDA in ECIME system is the directly electrocatalytic redox and indirectly mineralization by OH which generated in situ.There is alternative of the degradation of BX and DDA under low potential.Specific studies indicated that DDA exhibited electrochemical sluggishness and it was difficult to degrade in ECIME system under low potential.The degradation of DDA obviously needed higher voltage and current input with large energy consumption.Under the condition that the voltage of external electric field is 35V and reaction time of ECIME is 70 min,the removal efficiency of BX and DDA is 98.8%,80.7%,respectively.The removal of BX,DDA by self-flocculation shows negative effect.The cyclic voltammetry(CV)analysis showed that BX and DDA can degradate directly by electriccatalytic redox in ECIME system.And ECIME system can generate ·OH in situ the indirectly mineralization of ·OH is important for the degradation and removal of flotation reagents.The degradation mechanism of ECIME remove BX and DDA is the combination of electriccatalytic redox directly and degradation of high redox active ·OH indirectly.The possible degradation pathway of BX and DDA in ECIME system was proposed by combining with identification of intermediate by GC-MS analysis and the chemical reaction feature of BX and DDA.(3)The dominant interaction mechanism of heavy metal ion and flotation reagents in ECIME system include the complexed of lead,zinc with BX,DDA,the high chemical potential of complexes,and the changing of chemical characteristics of composite solution system.Specific studies showed that the content of soluble Pb2+,Zn2+and BX distribution in the lead-zinc flotation wastewater was significantly decreased due to the complex between heavy metals and flotation reagents.While the soluble DDA and COD distribution has no significant changing,but their species distribution varies greatly.The removal characteristics of Pb2+ and Zn2+ in composite system is different from the single lead-zinc system,but the overall removal efficiency of Pb2+ and Zn2+ had no significant difference between these two system.For the degradation of flotation reagents in the composite system,the existence of lead,zinc ions made the needed voltage increase slightly for degradation of BX completely.But it strongly inhibited the removal of DDA which refractory itself.So that the decomposition of DDA greatly depends on the high voltage inputs and the cost of energy consumption is greatly.(4)(BX)2M,(DDA)2M complexes which generated by the complexed between lead,zinc and BX,DDA are characterized by higher chemical potentials,stability,and poor solubility.This change of characteristics made DDA which refractory itself shows higher electrochemical stability in ECIME system under low voltage inputs.Specifically,the complex reaction is against to the reduction deposition of Pb2+,Zn2+and the degradation of BX,DDA.But the complex reaction was beneficial to the removal of both by flocculation with iron hydroxyl compounds.However,the removal efficiency of DDA by flocculation is very low.Pb and Zn loaded activated carbon materials can promote the complex adsorption of BX and DDA on interface of activated carbon and solution,which promotes degradation of BX while inhibits DDA,under the condition voltage of 18V.Research shows that(DDA)2M complex has higher stability in ECIME system,and reflecting as it needed a higher power input(voltage higher than 45V)and there is a temporal hysteresis for DDA degradation.(5)Based on the above research finding,this study put forward the concept of selective removal of Pb2+,Zn2+,BX and DDA from lead-zinc flotation wastewater by potential control of ECIME system,and optimized the parameters.Specifically,the method of selective removal means lead,zinc and BX removed efficiently while DDA retained by potential control in ECIME system,which according to the removal differences of Pb2+,Zn2+,BX and DDA in Lead-zinc flotation wastewater and the differences effect of them on Lead-zinc flotation process and the requirements of Lead-zinc flotation process reuse water.(6)The optimal parameters of selective removal of Lead-zinc flotation wastewater by potential control in ECIME system were obtained through the response surface method(RSM)design of experiments.Under the optimal conditions,the removal rates of Pb2+,Zn2+ and BX were 99.56%,99.77%and 98.79%,respectively,and the DDA residual rate was 92.07%.Research conclusion could provide a theoretical guidance for low-cost treat flotation wastewater and zero-discharge for non-ferrous metals flotation wastewater treatment especially lead-zinc flotation wastewater treatment.