Research on evaporation concentration and crystallization characteristics of electroplating wastewater: KCl Solution

• A heat and mass transfer model for KCl solution was developed. • The reliability of the model was verified by the corresponding experimental system. • Performance of wastewater evaporation concentration and crystallization was studied. • The optimal flow range of the KCl solution is 5.21 - 5.22 L/h. Electroplating wastewater contains various harmful substances, and its efficient treatment enables the recycling of industrial water and the complete recovery of water resources. Currently, there is almost no research related to KCl as electroplating wastewater. Based on single-droplet evaporation concentration and crystallization theory, this paper proposes a heat and mass transfer mathematical model for the concentration and crystallization process in a spray evaporation tower, using KCl as the solute in the wastewater. To verify the accuracy of the model, experiments were conducted using a spray evaporation crystallization tower to fit the Nu and Sh numbers of the wastewater solution in the non-crystallization and crystallization stages. The maximum relative error of the mathematical model was within 10%, which validated the accuracy of the model. In addition, effects of wastewater concentration, flow rate, wastewater and air inlet temperature on the evaporation concentration and crystallization performance of electroplating wastewater were also experimentally investigated. The results show that an optimized flow rate of 5.2174 L/h was required to maximize the oversaturation index, industrial water recovery rate and evaporation rate of tower of the wastewater when KCl was used as the solute. For low concentration wastewater (10%-20%), increasing the inlet temperature of wastewater and air is beneficial to its evaporation concentration and crystallization performance. For high concentration wastewater (25%-30%), when the air temperature is 140 ° C and the wastewater inlet temperature is 45 ° C, crystalline material has been formed in the outlet wastewater, indicating that the drying limit of this spray evaporation crystallization tower has been reached.