A comprehensive treatment method for seawater or concentrated brine

Abstract

The invention relates to a comprehensive treatment method of seawater or concentrated brine, which adopts the following steps: pretreatment, low cut-off nanofiltration separation, low cut-off nanofiltration permeate treatment, reverse osmosis concentrated water treatment, nanofiltration permeation permeate treatment and nanofiltration Filter concentrated water treatment. The method of the present invention reclaims fresh water completely, and the output of low-value magnesium chloride and calcium sulfate (gypsum) by-products is greatly reduced, avoiding the generation of low-value sodium sulfate, magnesium bromide, etc., and high-purity sodium chloride, calcium chloride, potassium sulfate The output of high-value products such as , magnesium sulfate, etc. has increased significantly.

Description

technical field [0001] The invention belongs to the fields of seawater desalination, comprehensive utilization of seawater resources, comprehensive utilization of salt lake or underground brine resources, etc., and specifically relates to a comprehensive treatment method for seawater or concentrated brine. Background technique [0002] my country is rich in marine resources and brine resources. According to relevant statistics, the underground brine resources along the Bohai Sea alone can reach 10 billion m 3 Left and right, which contain abundant and cheap water resources and chemical element resources. At present, my country's development and utilization of marine and brine resources are mainly based on seawater desalination, salt production, and salt chemical production such as soda ash and chlor-alkali. Combining various industries, comprehensive utilization of seawater and brine resources is carried out, and circular economy and sustainability are adopted. The road to d...

AI Technical Summary

Problems solved by technology

Due to the high salinity of concentrated seawater (nearly twice that of ordinary seawater) and the presence of pretreatment chemicals, a large amount of direct discharge into the sea will cause marine ecological pollution; it also wastes freshwater resources and various salt resources in concentrated seawater

[0005] (2) The combination of traditional salt field tanning and salt chemical industry is the mainstream way of comprehensive utilization of marine and brine resources, but there are shortcomings such as being seriously affected by seasons, relying on a large number of salt fields, and low resource utilization.

Since ordinary nanofiltration membranes have a relatively high rejection rate for all divalent ions, sulfate ions and calcium ions that are prone to scaling are mainly retained on the concentrated water side of nanofiltration. The use of ordinary nanofiltration membranes in the patent can effectively reduce the The risk of fouling of the follow-up concentration equipment of the filtered permeate, and the improvement of the purity of the solid salt, etc., but when using this method to treat the feed liquid with high calcium ion and sulfate ion content (such as concentrated seawater by-products of seawater desalination plants, underground brine, etc.) , the yield of nanofiltration permeate will be very limited, because ordinary nanofiltration membranes do not have the ability to fundamentally and selectively resolve sulfate ions and calcium ions in them. If the concentration multiple is increased, ordinary nanofiltration may cause Calcium sulfate scaling on the concentrated water side of the membrane, so the economical maximization of the seawater comprehensive treatment process cannot be realized

At the same time, the ordinary nanofiltration concentrated water obtained by using the patented process route is enriched with a large number of divalent ions, especially sulfate ions and calcium ions that are easy to scale. Even if the nanofiltration concentrated water is subjected to multi-effect evaporation or steam compression Distillation-seed method concentrates crystallization, calcium ions in the concentrated water (that is, more than 68% of the calcium ions in the raw material liquid) and most of the sulfate radicals will still be almost worthless calcium sulfate (rather than the higher value CaCl 2 , MgSO 4 etc.), and the equipment has the risk of fouling, so it is only piled up as waste (partially used as building materials or used for land reclamation), which is a serious waste of resources

Therefore, the introduction of ordinary nanofiltration process into the process of membrane or thermal desalination can only solve the problem of calcium sulfate scaling when the nanofiltration permeate is concentrated in depth, and can obtain pure concentrated brine with a high concentration. The recovery rate does not increase, and the comprehensive utilization still loses sulfate ions and most of the calcium ions in seawater, and still mainly produces magnesium chloride, which has low market acceptance rather than mainly producing magnesium sulfate (chlorine-free fertilizer). High degree of product

In addition, ordinary nanofiltration cannot be used directly for concentrated brines with high concentration such as concentrated seawater or underground brine (salt water concentration ≥ 8%), and it is only suitable for situations with low salt concentrations

[0010] In summary, the current conventional treatment processes for seawater and concentrated brine cannot avoid the scaling problem of calcium sulfate, the problem of a large number of by-products of low-value calcium sulfate salt, and the problem of not being able to obtain high value-added products such as potassium sulfate and magnesium sulfate; high value-added The extraction technology of salt resources in seawater and brine remains to be further developed

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