Enhanced Precipitation-filtration Process For Nickel-containing Electroplating Wastewater Treatment

Currently chemical precipitation method is the most frequently used application for processing nickel contained electroplating wastewater. Coagulant, coagulant aid and pH value modifier are added into the reaction system, which resulted in production of large amount of sludge difficulty in recycling of heavy metals. Ion exchange process is able ensure the expelled water concentration reached standards while the application is restricted in usage due to high cost. Heavy metal pollution in China has been very prominent attributed to increasing emissions of heavy metal wastewater year by year. It is extremely urgent to find an effective and economic method for the treatment of heavy metal wastewater. In this study,"strengthening sedimentation-filtration-ion exchange" process was introduced based on chemical precipitation method, which lay emphasize on processing performance and parameter optimization of each unit of the process. Then further research on treatment effectiveness of overall process on actual electroplating wastewater process as well as analysis of its applicability was taken.We concentrated on parameter optimization and sedimentation approaches strengthening of the reaction between nickel contained wastewater and sulfide. Research results showed that when the inlet concentration of nickel ion, suitable dosage of sodium sulfide to nickel and reaction time was controlled at580mg/L,1.2:1and20min, respectively,3.63mg/L of nickel ion concentration in expelled water and99.4%of removal rate was achieved. Simultaneous addition and mechanical stirring should be processed for wastewater and agents during the experiments. Pre-addition of sediment with ratio higher than10:1would effectively improve sedimentation effect of sludge. After settlement for20min, total Ni concentrations in supernatant and SS value were53.8,338and41.2mg/L,2060mg/L, separately for the samples with and without pre-addition of sediment. Coexisting ions in wastewater has no obvious influence on the precipitation effect.We studied the filtering effects of fiber quartz sand on the non-precipitated particles in the supernatant after strengthening precipitation. Research results showed that the increase of packing density of fiber filter and hydraulic retention time was beneficial to improve filtering effect of fibers. When packing density, hydraulic retention time and operation time were controlled at46kg/m3,30min and3h, respectively, total nickel concentration increased to20.9mg/L in expelled water, which was not suitable for separated filtration. Prolonging of hydraulic retention time and increase of packing density was helpful to improve the expelled water quality of sand filter, while down-flow filtration effect was slightly higher than that of up-flow. Separated filtration could be achieved with80-100mesh number of sand filter since the total nickel concentration was relatively low of5-6mg/L. Head loss of fiber filter were significantly lower than that of quartz sand filtration, which was43.2and198cmH2O after operation for3h, respectively. Hyphenated technology of fiber filtration and quartz sand filtration would effectively reduce the head loss of sand filter, extend the operation cycle and reduce backwash frequency.Nickel concentration in expelled water has been greatly reduced after the process of strengthening sedimentation-filtration, the quality of expelled water could be further improved through the advanced treatment of ion exchange process. Strengthening sedimentation-filtration-ion exchange process performed excellent treatment results nickel contained wastewater. Total Ni concentration after the process was8.20and4.85mg/L for treatment for nickel contained wastewater with and without complexing agent. After subsequent treatment by ion exchange resin, nickel concentration of expelled water was lower than0.1mg/L, which could meet the discharge standards. Meanwhile, recovery rate of nickel was also higher than99.9%.This process could realize stable and standardized discharge of high concentration nickel contained wastewater as well as recovery of nickel, which show excellent economic benefit. The whole technological process is simple and beneficial to experience transformation, which perform certain value for promotion.