Research On Treatment Technology Of Freezing Electroplating Wastewater Based On Supercooled Water Dynamic Ice Making

Large amounts of heavy metals contained in electroplating wastewater are harmful to the environment and human health.Among the existing electroplating wastewater treatment approaches,the main one is the traditional chemical precipitation method,where the chemical agent is put in the treatment process which generates a large amount of sludge.The secondary pollution issue is of concern.The principle of the method is to increase and transfer pollutants,which is not in line with cleaner production requirements.But the electroplating washing wastewater is concentrated and then reused in the electroplating tank,which can achieve the goal of cleaner production.At present,the commonly used methods for the concentration treatment of electroplating washing wastewater are mainly reverse osmosis and evaporative concentration in China and abroad.Among the commonly used electroplating approaches,no matter the acid copper process,nickel oxide process,chrome plating process,for wastewater with a PH value less than 2,or the alkali copper process,zincates zinc plating process for wastewater with a PH value greater than 12,it exceeds the allowable PH range of the existing reverse osmosis membrane,making the reverse osmosis method applicable to very limited range of electroplating wastewater treatment.The evaporation concentration method has large energy consumption and high cost.Therefore,there is an urgent need to develop a new technology for electroplating washing wastewater treatment with wide applicability,low energy consumption,and compliance with cleaner production requirements.In this study,the freezing method was applied to treat the wastewater from electroplating and washing,and the dynamic ice making technology of supercooled water was used to recycle the water from freezing crystallization purification to the electroplating and washing tank or the pretreatment of electroplating.The wastewater from freezing concentration and washing formed the electroplating solution to be reused in the electroplating tank,which turned waste into treasure.Compared with the existing freezing water treatment technology,the newly developed supercooled water dynamic ice making method has the characteristics of high solute removal rate,low energy consumption and high water production rate.The main contents include:(1)The interface progressive static freezing method test proves the feasibility of the freezing method in treating electroplating washing wastewater.And the freezing method can treat electroplating washing wastewater in various processes.This paper aims to find out the main problems in the practical application of the conventional interface progressive freezing method for electroplating water washing wastewater,and explore a new method of freezing ice making in engineering applications.(2)By studying the mechanism of ice formation in frozen water,we find an new ice-making method with higher ice crystal purity and lower energy consumption.Combined with the classic nucleation theory,through the supercooled water ice crystal growth test and the supercooled water atomization test,a "hydrogen bond angle barrier" theory was proposed to explain the reason that water cannot be frozen at 0 ℃ but formed supercooled water.It is further concluded that the method of artificially promoting ice is by reducing liquid restraint,increasing the flow of water,forming hydraulic shock,and reducing the "hydrogen bond angle barrier".From this,an ice making method that can produce fine ice crystals at a maximum temperature of-0.5 ℃ is designed for freezing water treatment.(3)Through the experiment on the relationship between ice crystal size and solute removal rate,I find the most suitable ice crystal size: ice powder ice and ice floc ice with a thickness of about 1 mm is the best choice for water treatment method by supercooled water dynamic ice making technology.And the energy consumption for forming this form of ice is only 62% of the interface progressive indirect freezing method.Through the ice-water separation method research test,the most suitable ice-water separation method is selected: it is to conduct supercooled water dynamic ice making while gravity filtration is performed during the engineering application of electroplating washing wastewater.And the centrifugation method is a comprehensive consideration of impurity removal rate,energy consumption,and time-consuming optimization.The fresh water production rate can reach 59%,which is much higher than the conventional interface progressive indirect freezing method of 25%.(4)The most suitable freezing method electroplating water washing wastewater treatment process was determined through the test of three kinds of representative electroplating water washing wastewater by supercooled water dynamic ice making freezing method.And it is calculated that the total energy consumption of the entire processing process is less than 1/10 of the energy consumption of the pure evaporative concentration method.(5)The process design,core processor design,and overall treatment system design for the treatment of electroplating washing wastewater by the supercooled water dynamic ice making method were performed in order to solve the connection problem between experimental research and engineering application.The study identifies a core processor that can simultaneously complete the four steps of dynamic ice making,gravity filtration separation,centrifugal dehydration,and ice melting in one processing facility.Economic analysis using the acid copper plating process as an example shows that the calculated operating profit margin of the system can reach 1.5 times.The treatment of electroplating washing wastewater using supercooled water dynamic ice making method has great operating economic benefits,and provides a theoretical basis for electroplating manufacturers to use this system for electroplating washing wastewater treatment.