| This paper mainly study on electroplating waste that contain multiple metal ions, such asiron, copper, chromium, nickel, it is put forward the technological processes, leaching-chemicalprecipitation (fractional precipitation and coprecipitation)-separation of coprecipitation-recyclingprocess. Through this route, corresponding product are obtained in each extracted steps with highpurity, waste liquid and residue can up to the national discharge standard, the purpose of friendlyenvironment and reutilized resource can be come true finally.To avoid the organic matter that effect on the extraction of metal ions in waste, thensimulated solution are prepared to recovery valuable metals respectively by fractionalprecipitation method, while five influencing factors should be considered, such as pH value,stirring speed, stirring time, standing time, washing times. The first step is iron-removed process,when the pH value is adjusted from1.80to3.40, mixing speed at100r/min, mixing time at10min, standing time at5min, washing time is3, the recovery rate of100%for Fe; the second stepis coprecipitation of Cu and Cr, when the pH value is adjusted to5.50, mixing speed at100r/min,mixing time at20min, standing time at5min, washing times at3, the recovery rates of100%,91.29%for Cu, Cr; the third step is the seperation of Cu and Cr, a few12%ammonia spirit areadded firstly, then controlling mixing speed at100r/min, mixing time at10min, standing time at5min, washing time is3, Cu and Cr can be seperated completely; the fourth step iscoprecipitation of Cu and Ni, when the pH value is adjusted from5.50to6.30, mixing speed at50r/min, mixing time at5min, standing time at5min, the number of washing is3, the recoveryrates of100%for Cu, meanwhile about38.75%Ni is subsided with Cu; the fifth step is theseperation of Cu and Ni, they can be well seperated at varying degrees by the method ofvulcanizing agent precipitation and iron powder displacement, under the condition of strong acid,a few Na2S are added to a solution containing the Cu2+, the sedimentation rate100%for Cu,controlling the ratio of nFe/nCu, about97.58%Cu2+can be displaced to elemental copper by ironpowder; last step is the extraction of nickel, when the pH value is adjusted to8.90, otherconditions should be controlled at the same time, the recovery rates of100%for Ni.Taking sulfuric acid as the leaching agent to manage electroplating sludge, the result of thisstudy show that the liquid-solid ratio is2:1, the leaching temperature is35℃, the leaching timeis0.5h, and0.50mL of sulfuric acid per gram of waste, leaching twice, four kinds of metal ionscan be leached with highest rate. The best process conditions of each metal in simulationexperiments are used in actual electroplating sludge. The experimental results show that thesedimentation rate of89.06%for Fe, at the same time Cu, Cr, Ni can be precipitated for1.08%,9.12%,0.74%with Fe in iron-removed process; when come to coprecipitation of Cu and Crprocess, the recovery rate of89.75%,100%,20.28%for Cu，Cr, Ni, the entrained phenomenon is serious; ammonia water are used to separate the precipitation of Cu and Cr, results show that thecontents of Cu and Ni has no change in before and after separation, it is proved that this separatedeffect is better; in Cu and Ni extracted process, the pH value is adjusted to6.30, Cu in remainingsolution that can be recycled all, its deposition rate was99.24%, Ni was precipitated down for30.61%with Cu; under the optimum experimental conditions, the ratio of nFe/nCushould becontrolled by iron powder displacement method, the result show that about Cu2+for98.72%canbe displaced to elemental Cu and Ni haven’t started to deposit; the last step is the extraction of Ni,the deposition rate of99.18%for Ni when the pH value is adjusted to the theoretical value.Through multi-wavelength spectrophotometry, the contents of four kinds of metal ions (Fe,Cu, Cr, Ni) can be determined simultaneously. This method is simple, extensive color range, highaccuracy. The effect of the interference by possible existing ion of Ca, Mg, Zn for this methodwere discussed, the best absorption wavelength of the four metal ion were found out, the molarabsorption coefficient under the specific wavelength were determined, and the linear equationwere completely established. Because the content of metal ions could be varied strongly indifferent realistic samples, the lower limit of this method was studied. The experiment reslutsshows that the lower limit of Fe, Cu, Cr, Ni are5×10-4mg/mL,1×10-3mg/mL,5×10-3mg/mL,5×10-3mg/mL respectively. It will obtain the reliably quantitative effect when the concentrationof samples can exceed that.The metal ion concentration, purity, organic matter, crystallization properties of product inwhole process should be characterized by ultraviolet-visible spectra, infrared spectra, XRD, etc.Results are analyzed show that the concentration of each metal ions in waste liquid and its pHvalue meet the discharge national standard, the product of each step with high purity, goodperformance. For the problem of pH changes, a deep going was disscussed about sediment ofMx(OH)yand Mx(CO3)y, in order to reveal actual reasons of discriminating between theoreticalvalue and experimental value. |
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