Impurities Effect on Carbonate Reactive Crystallization for the Wastewater

Reactive crystallization designed to separate nickel or copper ion from effluents has been advanced for applying to actual industrial wastewater containing impurities. In the primary reaction of this method, metal sulfate solution reacts with sodium carbonate solution in a semibatch crystallizer. In the present study, during the process of nickel or copper ions incorporation, inhibitory effect on seed growth of impurities, like cobalt, manganese, zinc, and borate and phosphate ions, was investigated. Through the 8-hour reactive crystallization, obtained particles’ characters and metals removal efficient were examined. Considering analyses data on metal component ratio in produced crystals, metal ions initial uptake rate was found to be different by the kind of seeds and impurities. And the centrifugation was performed against obtained crystals aimed for examining target metal purity improvement. The results indicated that copper components can incorporate and remove other metal ions easily. In addition, when the anions are used as impurities, depending on the kind of anions, the effect of damaging the surface of seeds or producing many fine particles has been confirmed. 1. Introduction Metal ions in the wastewater have often been treated by coagulation and precipitation methods [1]. In this treatment, however, a large amount of sludge is produced and metal substances are disposed without recycling. Meanwhile, wastewater treatment technologies based on environmental crystallization have an advantage in collecting metal ions as solid crystals. For example, studies about metal ion separation and precipitation methods with the use of a fluidized bed reactor have been preceded [2–4]. Some metal ions were shown to be taken efficiently on seeds such as quartz-sands at an optimum pH. And in our recent report [5], in a study using semibatch crystallizer, we suggested that metal ions were recovered on seeds regularly and continuously at only particular seed inputs. Actually, in the industrial effluent, many kinds of metal ions are contained typically. Metal ions uptake mechanism somewhat relates to the adsorption or coprecipitation process. Some have found the order of metal ions adsorption strength to some base seeds [6–8], and others have examined the pH range at which metal ions can be selectively separated efficiently with the use of difference of solubility products in the process of co-precipitation [9, 10]. Thereby, in this paper, on the basis of nickel or copper ions crystallization in the regulated solution, seeds growth inhibition mechanisms by the