Study On Separation Of The Components That Tend To Scale In Acidic Wastewater Use Membrane Separation Technology

This paper dealt with the problem of pipeline scaling when wastewater from a phosphate fertilizer plant is transported back to the mine for mineral processing.Membrane separation technology was selected to treat the wastewater in order to reduce the concentration of scaling ions in the wastewater and solve the problem of scaling blockage in the pipeline.Firstly,the water quality and pipeline scale composition of wastewater from phosphogypsum slag site at different time were analyzed.The pH value of acidic wastewater fluctuated around 1.6².0.Compared with the previous wastewater,the scaling component K₂SiF₆ in the wastewater was in a state of oversaturation.Although the contents of Ca²⁺and SO₄^2-were reduced,but the concentration was still higher than the solubility of CaSO₄ in the wastewater.The main components of potassium fluosilicate and Calcium sulfate dihydrate were analyzed by XRD.It was known that H₃PO₄,H₂SO₄,H₂SiF₆,and HF in the wastewater were 3.26%,1.55%,0.489%,and0.34%,respectively,by carrying on acid-base titration to the wastewater.Secondly,the solubility of potassium fluosilicate in the temperature ranged from273.15K to 303.15K were tested in the analog mixed acid,with the increase of temperature,the solubility of potassium fluosilicate increased from 0.256g/L to1.172g/L.At the same time,regression fitting was performed on the solubility data,the solubility date of potassium fluosilicate were well correlated by Apelblat model and Empirical polynomial model,with the fitting accuracies of 0.9881 and 0.9819,respectively,between which Apelblat model was better than Empirical polynomial model.Then,the pretreatment effects of wastewater were compared which was treated with calcium chloride,aluminum sulfate and calcium oxide.The results showed that the removal rate of fluoride ion in wastewater treated with calcium chloride,aluminum sulfate and calcium oxide were 99.0%,98.5%and 99.3%respectively.The removal rate of fluorosilicate ions in wastewater treated with calcium oxide was 93.9%.Finally,the"ultrafiltration+reverse osmosis"process was used to treat the wastewater.The influence of ultrafiltration membrane flux caused by operating pressure,operating temperature,membrane surface velocity,the ratio of concentrate water to raw water was discussed,and the optimal operating conditions of ultrafiltration membrane for the treatment of acidic wastewater were determined,the removal rate of suspended solids and electrolyte in wastewater were also studied by this chapter.The turbidity of wastewater treated by ultrafiltration membrane is less than 1NTU,which would provide appropriate feedwater to reverse osmosis membrane.A mixed solution of sodium tripolyphosphate?STPP?and EDTA disodium salt was selected to clean the polluted ultrafiltration membrane,after cleaning,the membrane flux could be restored to more than 90%of the original membrane flux.Reverse osmosis experiments were carried out according to the operating conditions of ultrafiltration membrane.At the same time,reverse osmosis membrane fouling was evaluated,and the membrane flux remained above 60%of the original membrane flux until the completion of the experiment.The effects of chemical pretreatment,ultrafiltration membrane treatment,reverse osmosis membrane treatment were compared,and the results show that the concentration of scaling ions in wastewater treated with reverse osmosis membrane has dropped below its solubility,membrane separation technology used to treat the acidic wastewater has achieved the desired effect.