In China's industrial production, a large number of acidic or alkaline waste liquids are usually produced, which contain different concentrations of metal ions and acid-base. The direct discharge not only wastes resources, but also causes serious pollution to the environment. In order to protect the environment from pollution and to recover useful material, it is necessary to purify the acid and alkali waste liquid before it is discharged. Most of the treatment of this kind of waste water is neutralized at home and abroad, and this treatment is easy to cause secondary pollution. The new membrane technology, such as permeation, reverse osmosis, nanofiltration, ultrafiltration and dialysis, can effectively avoid secondary pollution.

As a new separation technology, membrane technology can effectively purify the waste water, and recycle the useful material, and has the characteristics of energy saving, low consumption, no pollution, simple equipment, convenient operation, so it shows broad prospects in terms of pH of the waste water treatment.
 
1. Acid environment

Acid solutions (part) that have been tested:

·   20% H₂SO₄

·   20% HCl 

·   30% H₃PO₄

·   4% HNO₃

Typical applications in acid environment:

·   Purify acid and remove metal cations

·   Recovery of acid after leaching operation

·   Mineral acid decolorization

·   Recovery of dissolved chemicals

·   Concentration and recovery of ions in an acid solution

·   Some conventional applications that need to be used for corrosive strong acid cleaning

·   Chemical industry: the recovery of acid and the final product in the process of producing acid medium

·   Food, beverage and dairy industry: purify the acid after the use of the CIP process and reuse in the process of production and the cleaning of equipment.

·   Recovery of metals from the extractive solution, such as copper, zinc, cobalt, molybdenum, tungsten, uranium, gold, etc..

·   Reducing the cost of operation and sewage treatment

·   Recovery of high value metals from emission and industrial waste water

·   Pre separation of copper and gold in the process of carbon slurry to improve the extraction rate of subsequent gold.

 
2. Alkaline environment

The tested alkaline solutions include:

·   4% NaOH

·   10% NaOH

·   20% NaOH

·   20% KOH

Typical applications in alkaline environment

·   Recovery of alkaline current (sodium hydroxide, potassium hydroxide)

·   Recovery of metal in alkaline flow

·   Recovery of used electrolyte

·   Reducing COD content before neutralizing industrial waste water

·   Recovery of alkaline solution for cleaning containers and equipment

·   Some conventional applications that need caustic alkali cleaning

·   Pulp and artificial fiber: purification of caustic soda from hemicellulose and other organic pollutants to make sodium hydroxide reusable up to 95%

·   Food, beverage and dairy products: Purification of waste lye washing flow (CIP) solution and regenerated solution (in Decolorization of sugar) after ion exchange, to make the repeated use rate of sodium hydrate up to 95%;

·  Chemical: alkali recovery and final product concentration used in many alkaline environmental production operations.