Study On The Removal Of Heavy Metal Zinc From Zinc Pickling Wastewater

China is a large country in the world that produces and consumes galvanized products.When galvanized products are produced,a large amount of zinc-containing pickling waste liquid will be produced.Because the heavy metal zinc and iron are close to each other on the metal activity table,and the relative atomic mass is not much different,the removal of heavy metal zinc has always been a research difficulty in the process of realizing the resource utilization of pickling waste liquid.The thesis studied the removal of heavy metal zinc from pickling waste liquid by phosphate precipitation method and tributyl phosphate(TBP)extraction method.The phosphate precipitation method explored the influence of various influencing factors such as pH and phosphate dosage on the effect of zinc removal.Tributyl phosphate extraction method explored the influencing factors of extraction time,hydrochloric acid content,phase ratio(O/A),extraction level,and the influence of these factors on the load of TBP zinc extraction and the recycling capacity of TBP.The results of the study are as follows:(1)Phosphate is usually used as stabilizer in the process of preparing coagulant from pickling waste liquid.The phosphate precipitation method is used to synergistically remove zinc from the pickling waste liquid,which can play the dual role of phosphate.While removing zinc,the excess phosphate can also act as a stabilizer without introducing new pollutants.In the study of removing zinc from ferrous chloride solution(ferrous iron content10%)by phosphate precipitation method,the initial zinc concentration of simulated waste solution was 5 g/L,10 g/L,20 g/L,and 50 g/L,the optimal zinc removal reaction conditions for the pickling waste liquid are: pH 1.3,1.3,1.2,1.0,and the dosage is expressed by the molar ratio of zinc to phosphate(referred to as the molar ratio of dosage),respectively 1:1,1:0.67,1:0.56,1:0.56,the reaction temperature is30 ℃,the reaction time is 60 minutes,the removal rate of zinc is 40.3%,36.3%,30.5%,26.7%,respectively.Under the same conditions,using the phosphate precipitation method to treat the actual pickling wastewater,the zinc removal rates were 40.8%,35.9%,30.0%,and 27.0%,respectively.Therefore,when the zinc content is less than 20 g/L,it is advisable to use the phosphate precipitation method to remove zinc in the pickling waste before preparing ferric chloride from the pickling waste.In the research of removing zinc in ferric chloride solution(ferric iron content10%)by phosphate precipitation method,the zinc concentration of simulated waste liquid is 5 g/L,10 g/L,20 g/L,50 g/L The optimal reaction conditions are: pH value is0.9,0.9,0.9,1.0,the molar ratio of dosage is 1:2,1:1,1:1,1:0.8,and the reaction time is 60 minutes.The reaction temperature is 30 ℃,and the removal rate of zinc is25.2%,27.3%,35.6%,49.5%,respectively.Under the same conditions,using the phosphate precipitation method to treat the actual pickling waste liquid,the removal rates of zinc were 24.6%,28.2%,34.6%,and 49.2%,respectively.Therefore,when the zinc content is higher than 20 g/L,it is advisable to use the phosphate precipitation method to remove the zinc in the pickling waste after preparing ferric chloride from the pickling waste.(2)In the study of removing zinc from ferrous chloride solution(ferrous content10%)by tributyl phosphate method,the optimal reaction condition for the initial zinc concentration of 50 g/L simulated solution is: hydrochloric acid content of 5%,The extraction time is 6 minutes,and the three-stage extraction(the first-stage extraction ratio is 1:1,the second-stage and the third-stage extraction ratio are 0.5:1).After the first-stage extraction,the removal rate of zinc has reached 79.1%.TBP’s zinc extraction load is 39.55 g/L,after three-stage extraction,the removal rate of zinc can be as high as 99.9%.Under the same test conditions,the zinc removal effect of TBP on the actual pickling waste liquid is consistent with that of the simulated solution.After the first level extraction,the zinc removal rate reached 79.3%,and after the third level extraction,the zinc removal rate reached 100%.The zinc extraction load of TBP is negatively correlated with the comparison,positively correlated with the initial zinc concentration,and negatively correlated with the extraction order,the fractional extraction effect is better than the single-stage extraction effect,but the fractional extraction number should not be too much.Using 7.5% sodium hydroxide solution,under the conditions of 1:1 ratio(O/A),stripping time of 6 minutes,and level 1 extraction,the TBP solution after zinc extraction was subjected to a stripping test,and the stripping effect reached 100%,and the TBP after stripping still has good extraction ability.