Experimental Study On Advanced Treatment Of High Chlorine Circulating Cooling Water In Iron And Steel Enterprises By Reverse Osmosis Technology

The low water resource recycling rate in China’s steel enterprises has become one of the main factors restricting their comprehensive competitiveness.There is a large concentration of chloride ions in the circulating water used for indirect cooling of equipment in steel enterprises.Long term cyclic use not only leads to pipeline scaling and corrosion,but also leads to serious environmental pollution problems such as soil salinization and alkalization.Therefore,based on conventional water treatment and reuse technologies,it is no longer possible to meet the goal of deep treatment and reuse of wastewater in steel enterprises.Introducing the Reverse Osmosis（RO）desalination process for deep treatment of high chlorine circulating cooling water in steel enterprises is of great significance to achieve the reuse of high chlorine circulating cooling water,reduce water consumption per ton of steel,and improve economic benefits of steel enterprises.This article takes the deep treatment of high chlorine circulating cooling water in steel enterprises using RO technology as the research objective,and evaluates the treatment capacity of RO equipment for high chlorine circulating cooling water using membrane flux and retention rate as evaluation indicators.The effects of operating temperature,operating pressure,feed p H,feed flow rate,and Na Cl concentration on RO membrane separation efficiency are clarified;Based on the response surface experimental research method,the influence of different levels of operating temperature,operating pressure,and feed p H on RO membrane flux and retention rate was analyzed.A mathematical model was established and optimized design analysis of the three factors was conducted to determine the theoretical optimal process parameters.The results indicate that an increase in operating temperature is beneficial for improving membrane flux;The increase in operating pressure and feed p H can simultaneously improve RO separation performance;The flow rate of the feed liquid has little effect on the membrane separation performance;The effect of influent Na Cl concentration on membrane separation performance is extremely significant.In the response surface experiment,when the operating temperature is 26℃,the operating pressure is 0.7 MPa,and the feed p H is 8,the theoretically optimal RO separation effect can be obtained as a membrane flux of 23.074 L·m^<sup>-2·h^-1.The interception rate of is 96.428%.After experimental verification,the error between the predicted value and the actual results is small,indicating that the model can better predict the actual situation.Using scanning electron microscopy,Fourier transform infrared spectroscopy,X-ray diffraction and other methods to analyze the reasons for the decline in performance of the RO membrane during its later use and the pollution mechanism during the RO process.Based on the Solution Diffusion（SD）model and membrane theory,the complex transport phenomena of water molecules and salt ions during the RO process were studied.The results show that membrane fouling is mainly manifested by light yellow inorganic substances attached to the side and surface of the membrane,and the main phase components of pollutants are Ca CO3,Na Cl,Ca Cl2,and Na2SO4.In the later stage of RO membrane operation,there was a significant concentration polarization phenomenon.The concentration polarization factor of Na Cl solution with a concentration of14000-18000 mg/L ranged from 1.12 to 1.17,and the true concentration of salt ions on the membrane surface,CRm,was 1.1 to 1.2 times that of the original solution.Due to the concentration polarization phenomenon,the true concentration CRm of salt ions on the membrane surface is higher than the main concentration CR of the feed liquid.The concentration polarization correction factor is always less than 1,and the Bcp/B under experimental conditions is 94.22-97.79%.The increase in membrane flux significantly decreases,and the larger the membrane flux,the greater the difference between the actual mass transfer coefficient Bcp and the apparent mass transfer coefficient B.