| As a kind of dangerous waste containing a large number of valuable heavy metal, electroplating sludge is valuable on the utilization in the resources along with the social development. Furthermore the separation of matals fom the electroplating sludge can make the dangerous solid waste into general solid waste and recycling. It is relatively low, environmentally friendly, low cost for biological treatment of electroplating sludge with low content of heavy metals. So this text trys leaching the metals from electroplating sludg by the Acidophilic Thiobacillus and Aspergillus niger, and separate and recovery of valuable metals in leaching solution.The treatment of electroplating sludge is bioleaching by Acidothiobacillus thiooxidans and Acidothiobacillus ferrooxidans on solid 3%. Its leaching rate of Ni, Cr and Cu can reach the 92.9%,85.1% and 96.8% respectively, and is higher than the sulfuric acid leaching system leaching rate with the same pH(especially Cr). But it can not apply to engineering for its long term (15 d after domestication). However the inorganic acid which is got by by Acidothiobacillus thiooxidans and Acidothiobacillus ferrooxidans using municipal waste sludge on solid of 1% can leach Ni, Cr and Cu effectively at a shout time of 2 h, and it can reach the same levle of the sulfuric acid with the same pH, and it can low much of cost, and the cost of leaching of electroplating sludge by acids produced by A. thiooxidans TS6 is less than sulfuric acid. It is effective to separate and recovery meatls by controling the pH using NaOH for an inorganic acid leaching solution. In details, it can separate and precipitate Fe at the pH of 2.8 almost, it can control the pH=5.8 or a lower little in order to get the more precipitation of Ni before to precipitate Ni, it can control the pH=5.8 or a higher little in order to get the mre pure precipitation of Ni before to precipitate Ni correspondingly. So, Chemical precipitation method which can efficiently separatie and recovery valuable heavy metals of Ni, can make the recovery rate reach 82. 56%.It will get a bad treatment to use Aspergillus niger to leach the electroplating sludge directly, however it can get a leaching rate of Ni 91.9%, Cr 74.4% and Cu 55.2%for 6 d of bioleaching treatment after puting the electroplating sludge into Aspergillus niger at the ninth day of culture. Furthermore, the citric acid and glucose secreted by A. niger Y9 is the main organic acids whcih promotes the leaching of heavy metals electroplating sludge. The organic acid produced by Aspergillus niger in pure culture for 15 d leach electroplating sludge only for 4 h to make the leaching rate of Ni, Cr and Cu reach 85.0%,63.8% and 57. 9%. Four kinds of organic acids on Ni, Cr, Cu leaching effect are:citric acid> malic acid> oxalic> gluconate; four acid in the mixing process, can be considered neither antagonistic nor synergistic additive effect almostly. So bioleachig by organic acids produced by A. niger Y9, such as citric, has the advantage of short time, and it has better prospects for engineering applications. For organic acid leaching solution, Chelex-100 resin can be effectively adsorbed organic acids leaching solution of electroplating sludge for Ni and Cu, and it can separate form Cr greatly. HCl can be effectively resolvedusing the heavy metals Ni and Cu adsorbed by Chelex-100 resin, so that the Chelex-100 resin can obtain a higher reuse rate, but it requires a higher concentration of HCL to resolve Cr. The leaching solution of electroplating sludge after adsorbent of resin can again leach electroplating sludge after controling its pH with HCl to the same level before its leaching treatment, and it can leach heavy metals effectivly and low much of the cost.For the cost analysis, the treatment process is finally adopted:the eventual adoption of A. thiooxidans TS6 acid treatment of electroplating sludge, then separated and recovered by chemical precipitation of heavy metals. |
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