Study On The Extraction Process Of Reverse Osmosis Seawater And Highly Concentrated

Water resource is in short supply,desalination has become an important way to solve water crisis.Currently mature desalination methods are mainly two types of thermal and membrane.Wherein the former is mostly used for the regions of lower energy prices and situations which have more waste heat available,in all other situations are generally used membrane method,especially in recent years more and more mature and efficient seawater reverse osmosis?SWRO?process.With the increasing of human needs for fresh water,desalination plants are on a large scale,the emissions of high concentration saline causes serious ecological disaster.From an economic standpoint,seawater is rich in mineral chemistry scarce,directing emissions is a waste of resources.If the part of the brine can be used,not only eliminate the ecological pressure,but also achieve the rich mineral resources of salt,sodium,magnesium and the like.For this reason we design a set of comprehensive development process of reverse osmosis include chemical treatment,precipitation and membrane separation.The main work is as follows:?1?Analyze the composition of reverse osmosis seawater.The sea is very complex and must be accurately analyzed.In the study sea crystal is used to simulated seawater reverse osmosis.Then analyze the anions and cations by various methods.Finally a result is obtained that the cations of concentrated seawater are mainly Na⁺,K⁺,Mg²⁺,Ca²⁺and Sr2+and the mainly anions are Cl^-,SO₄^2-,Br-and OH^-.?2?Extract the magnesium and calcium of concentrated seawater.Adding sodium hydroxide to the reverse osmosis to extract magnesium and adding sodium carbonate to remove calcium.The removal rate of Mg²⁺ is 99.88% and the removal rate of Ca²⁺ is 99.76%.Mg²⁺ and Ca²⁺ are removed and avoid the fouling problem by this way.And obtain the product of Mg?OH?2 which only contain 1.66% of the Ca²⁺ impurity.Recycling and reusing Mg?OH?2 has economic benefits?3?Remove sulphate of concentrated seawater by the technology of nanofiltration.Achieve the separation of NaCl and Na2SO4 mixed solution after the solution enter the nanofiltration membrane.At the recovery of 94.12%,the permeate is mainly NaCl,wherein the content of SO₄^2-is less than 5% in the total composition which can be directly made salt by electrodialysis.The concentrate is mainly Na2SO4,which can be produced sulfate solid to obtain economic benefits.?4?Concentrate the reverse osmosis to make salt by the way of electrodialysis.Achieve 18% of NaCl concentrated water and 3% NaCl brackish water by electrodialysis.The cost of obtaining a ton sodium chloride by electrodialysis is 36.44$ in the optimal conditions.Then put the concentrated water into MVR evaporator,the cost of one ton sodium chloride is 15.17$.Synthesize the two items costs,the cost of per ton sodium chloride is only 51.61$ which is lower than the cost of reverse osmosis seawater directly entering MVR evaporator to obtain salt.