Experimental Study On Membrane Integrated Process For Treatment Of Simulated Metallurgical High-salt Wastewater

About 15000m³/d high-concentration saline wastewater,which produced in one company's production system,were treated by degreasing,homogenization,adjusting,pre-sedimentation,air flotation,Sulfide precipitation and filtration,then could meet the national discharge standard with its inside heavy metals and organics were removed and recycled.However,the salinity of the treated water was too high,outflowing without treatment will cause serious land salinization and environment pollution,as well as will waste a lot of inorganic salts.Therefore,it is of great economic and environmental benefits to carry out efficient research on the utilization of high-salt wastewater,such as achieving the zero discharge of metallurgical high-salt wastewater and the resource-use of inorganic salts.In this paper,the coupling process of nanofiltration-reverse osmosis-refrigeration denitration was chosen,and the resource-use of inorganic salts in high-salt wastewater was researched.The influence of process parameters at various stages on the separation result was analyzed,and the optimal parameters at each section were confirmed.All of this will establish foundation for the industrial application of this technique.Adopting the nanofiltration technology,the effective separation of NaCl and Na₂SO₄ was achieved for simulant high salt wastewater.The effect of concentration ratio,pressure,flow rate and temperature for membrane separation performance of nano-filter section was studied,which showed that all these four factors can affect the separation performance of nanofiltration membranes and it was different among these effects.The retention rate of SO₄^2-was always over 99%and rate of Cl^-maintained between 20%⁴0%in all above situation.When Na₂SO₄concentration was fixed by 40 g/L,these factors were ranked in order of importance in the light of effecting the separation performance of nanofiltration membrane:working pressure>working temperature>concentration ratio>flow rate.NaCl:Na₂SO₄=35:40,working pressure3.0 MPa,flow rate 8 LPM,and temperature 30?was considered the optimal solution.The successful separation of NaCl and Na₂SO₄ was realized,[Na₂SO₄]/[NaCl]?18.51 in the water separated by nanofiltration section under the optimal solution.For nanofiltration permeate,the use of the reverse osmosis process realized the effective recycling of NaCl.It studied the influence of concentration ratio,pressure,flow rate and temperature on separation performance of reverse osmosis membrane.The experiment results showed that all these four factors can affect the separation performance of reverse osmosis membrane for varying degrees,though the retention rate of SO₄^2-and Cl^-were always over 99%and 98%for the reverse osmosis membrane,respectively.The sequence of primary factors which affected the separation performance of reverse osmosis membrane was working pressure>concentration ratio>flow rate>working temperature.The best choice were NaCl concentration5 g/L,working pressure 3.0 MPa,flow rate 10 LPM,temperature 30?.NaCl purity was above97.5%after the recycling the simulated wastewater by nanofiltration-reverse osmosis coupling process and it met the requirements of secondary refined industrial salt specified in industrial salt?GB/T 5462-2015?.The refrigeration denitration was employed to get the effective recycling of Na₂SO₄ in nanofiltration concentrated solution.The influence of concentration multiple,refrigeration temperature and refrigeration time on product purity and recovery was investigated and the results showed refrigeration temperature,concentration multiplere and frigeration time in turn affected the product purity and recovery,but these 3 factors had little effect on product purity which always maintained above 98%.At refrigeration denitration section,the best working conditions were concentration multiple 4.5 times,refrigeration temperature 0?,and refrigeration time 120 min.In order to improve the output recovery rate of Na₂SO₄,the experiment was optimized by the step-by-step refrigeration denitration technology and the results showed that the recovery of Na₂SO₄ increased 6.39%higher than that previous.