Study On Resourcefulization Of Heavy Metals Electroplating Sludge And Its Application

Electroplating sludge is one of hazardous wastes according to the regulations of the state.The heavy metals in electroplating sludge are not stable and easily run into water, resulting inenvironmental pollution and indirect threat to human health. However, the heavy metals inelectroplating sludge have recyclable value. If electroplating sludge can not be treatedreasonably, it will cause waste and loss of resource. At present, the most of electroplatingenterprises in China use landfill technology to deal with electroplating sludge, which can notrecycle the heavy metals and cause resource loss and potential environmental contamination.Therefore, study on resourcefulization of heavy metal electroplating sludge will havesignificantly environmental, resource and social values. At the same time, heavy metalsresourcefulization is a sustainable technology.At first, the basic properties of electroplating sludge were analyzed. The heavy metalsions in electroplating sludge were leaching out by sulfuric acid as the leaching agent. It wasprepared for the next resourcefulization. Heavy metal resourcefulization were done throughtwo different methods, step by step precipitation process and ferrite process. At last, thearsenic adsorption removal performance of the composite ferrite from electroplating sludgewas studied. The main results are as follows:(1) The properties of electroplating sludge are as follows: water content is73.60%, pHvalue is7.6, the contents of Cu, Fe, Ni, Cr are12.86%,2.45%,3.32%and0.58%,respectively. The leaching content of copper in toxicity characteristic leaching test is muchmore than the required standard. Sulfuric acid was chosen as the leaching agent forelectroplating sludge. Under the condition as that liquid-solid ratio is5:1, the temperature is25oC, the time is60min, the leaching rates of Cu, Fe, Ni, Cr were98.72%,85.81%,97.65%and97.83%, respectively. The acid leaching residues of heavy metals are less than theregulatory limit in the toxicity characteristic leaching procedure. The residues can belandfilled safely.(2)Step by step recyclization process of heavy metals consists of copper precipitationremoval by sodium sulfide, precipitation removal of iron and chromium by phosphate andnickel by carbonate. Copper precipitation by sodium sulfide results in crude copper sulfide.The copper precipitation rate is97.36%, the nickel loss rate is4.92%. The removal procedureof iron and chromium by phosphate precipitation shows that the removal rate of iron andchromium are96.45%and99.06%, respectively. Nickel precipitation by carbonate shows thatthe recyclization rate of nickel is79.68%. The optimum preparation conditions of ferrite fromelectroplating sludge leachate are that Fe/M is8, M is the heavy metals in leachate, pH valueis9, temperature is80oC, the reaction time is120min. The resulted composite ferrite wascharacterized by XRD、SEM、BET and Zeta potential.(3) The performance of the composite ferrite prepared from electroplating sludge toadsorption removal of arsenic was studied. The effects of the initial pH of solution and theco-existing ions were discussed. The results show that the removal rate of As(V) is above95%in the range of pH3～7, the alkaline condition is disadvantageous to As(V) adsorption. The co-existing ions of Ca2+and Mg2+have no effect on the adsorption of As(V). Theco-existing ion of CO32－has significant impact on the adsorption of As(V), which can beinhibited by adjusting pH within the range of3～5. The adsorption kinetics and equilibriumadsorption isotherms indicate that the adsorption process follows the pseudo-second orderreaction model and Langmuir model. The adsorption capacity is25.98mg/g. The desorptionand regeneration properties of composite ferrite were investigated. The results show that thedesorption rate is94%when using2mol/L sodium hydroxide as the desorbent and with onehour of reaction time. Sodium hydroxide can be used as a good desorbent to As(V). Theremoval rate is cut down15%when composite ferrite is used as adsorbent for five times.Composite ferrite has a certain valuable of recyclization.In conclusion, the step by step precipitation process deals with acid leachate fromelectroplating sludge to obtain crude heavy metal precipitates. The heavy metals can berecycled to some extent. The crude heavy metal precipitates contain impurities. However,ferrite process makes heavy metals embed into spinel structure and form stable compositeferrite. The prepared composite ferrite exhibits good adsorption removal performance toAs(V). Therefore，ferritization is a promising resourcefulization procedure for electroplatingsludge.