| With the rapid development of industry,China's economy had grown rapidly,but at the same time it had brought many environmental problems.The problem of urban black and odorous water was particularly prominent.The pollution of heavy metals in river bottom mud was one of the problems to be solved.Once the heavy metal entered the water body,it not only polluted the water body,but also enriched it in the sediment of the river surface through a series of functions.When the environmental conditions changed,part of the heavy metals could be released from the sediment,causing secondary pollution of the water.The accumulation of heavy metals in the sediment not only posed a serious threat to aquatic organisms,drinking water in the rivers and farmland,but also threatens human health through the food chain.Therefore,how to removed the heavy metals in the river sediment had become a problem to be solved.In this experiment,a black odorous water body sludge in Wuhan was used as the research object,and the traditional chelating agent EDTA and the green chelating agent dicarboxymethyl alanine were used.Sodium(MGDA)and glutamic acid N,N-diacetic acid(GLDA)were used to wash heavy metals Cd,Cu and Ni in sludge,and compared with four factors influencing time,dosage,pH and leaching times.The removal effect.Traditional chelating agent EDTA leaching heavy metals.At room temperature,pH=3,rinsing time is 24 hours,EDTA and heavy metal molar ratio EDTA:M=5:1(the same below),under the experimental conditions of rinsing 3 times,the traditional chelating agent EDTA on heavy metals Cd,Cu Ni had the highest removal rate of 81%,63%,and 80%,respectively.Study on the leaching of heavy metals by the green chelating agent GLDA.The optimal experimental conditions for the removal rate of heavy metals by GLDA were: pH=3,rinsing time is 16 h,GLDA:M=4:1,rinsing 3 times,the removal rates are 74%,60%,81%,respectively.Study on the leaching of heavy metals by the green chelator MGDA.Under the optimal experimental conditions of room temperature system,pH=3,rinsing time 16 hours,MGDA:M=5:1,rinsing 3 times,the highest removal rates of the three heavy metals were 75%,62%,80%,respectively.The three chelating agents havd good removal effects on heavy metals in the sediment.According to different influence factors,the removal efficiency fluctuates.With the increase of rinsing time,the removal rates of heavy metals Cd,Cu and Ni were all shown.Increasing the trend,with the increase of time,the removal rate will eventually reach a relatively stable;the amount of chelating agent will also affect the removal rate,the amount of chelating agent will increase,and the removal rate will increase.After reaching a certain amount,the removal rate will be stable;pH was the main factor affecting the removal rate of heavy metals Cd,Cu and Ni.When the system was under acidic conditions,due to the acidification of the solution,the amount of protons in the solution was more,and the removal effect of heavy metals was better.When the system was neutral or alkali Under the condition of the condition,the removal rate of heavy metals was poor.When the pH of the system was under strong alkali conditions,the removal effect was not good.With the increase of the number of leaching,the chelating agent could achieve the removal effect by changing the form of heavy metals.The best chelating agent for heavy metal removal was EDTA.GLDA was superior to MGDA in removing heavy metal Cd.MGDA was superior to GLDA in removing Cu and Ni.All three chelating agents change the form of heavy metals to changed the heavy metals from an insoluble state to a soluble state,thereby achieving a removal effect.The three chelating agents had good removal effects on the weak acid extraction state,oxidation state and reduction state of heavy metals Cd,Cu and Ni,and the removal effect on the residual state was poor.Through the precipitation of Na2 S,the heavy metals in the leaching agent GLDA and MGDA can be recovered,so that the waste eluent could be directly discharged. |
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