The main methods for poduce poly aluminum chloride
There are three main methods for producing polyaluminium chloride:
1. Drum-type polyaluminum chloride has average aluminum content and high water-insoluble matter, and is mostly used for sewage treatment.
2. Plate and frame type polyaluminium chloride, with high aluminum content and low water-insoluble matter, is used for municipal sewage treatment and domestic sewage treatment.
3. Spray-dried polyaluminum chloride has high aluminum content, low water-insoluble matter, and fast dissolution speed. It is used for drinking water and higher standard water treatment.
According to the production process, it can be divided into acid method, subtraction method, neutralization method, pyrolysis method, pressure reaction method, mixed gel method, electrodialysis method, electrolysis method, etc. Solid polyaluminum chloride is obtained by spray drying or drum drying liquid polyaluminum chloride. Spray drying is an ideal drying method.
At present, the main methods for producing polyaluminum chloride in my country are: metal aluminum (including aluminum ash, lead slag) method, activated aluminum hydroxide method, aluminum trioxide (including bauxite, coal gangue, etc.) method, crystallized aluminum chloride Law etc.
1. Metal aluminum method
The raw materials used in the metal aluminum method are mainly aluminum scraps, aluminum ash and aluminum slag left over from aluminum processing. In terms of technology, it can be divided into three types: acid method, alkali method and neutralization method. At present, most of the manufacturers in my country that use metallic aluminum as raw material to produce polyaluminum chloride adopt the acid method.
(1) Acid method
The acid method has the advantages of fast reaction speed, low equipment investment, simple process, and convenient operation. However, the impurity content in the solution is relatively high, especially the content of heavy metal elements that often exceeds the standard. The product quality is unstable and the equipment is severely corroded.
(2) Alkali method
The alkaline production process is more difficult and requires greater investment in equipment. Due to the large amount of alkali used and the need for a large amount of hydrochloric acid to neutralize to pH=4-5, the cost is high and its application is subject to certain restrictions.
(3) Neutralization method
The neutralization method is characterized by combining the advantages of both the acid method and the current method. The key to the neutralization method is that when synthesizing polyaluminum chloride, the ratio between sodium aluminate and aluminum trichloride solutions must be strictly controlled to ensure that the alkalinity meets the standard requirements.
2. Aluminum hydroxide method
The raw materials used in the aluminum hydroxide method are mainly active oxygen alumina in the Bayer process of aluminum smelting. During production, excess active aluminum hydroxide and hydrochloric acid are used to react at relatively high temperature (50-180°C) and pressure (0.5MPa) to produce a liquid polyaluminum chloride product with a basicity of 41.6-48.6%, which is then processed Concentrate and dry to obtain solid polyaluminum chloride product.
3. Aluminum trioxide method
The main raw materials of aluminum oxide are gibbsite, bauxite, kaolin, coal gangue, etc. The first step of this process is to obtain crystalline aluminum chloride, and the second step is to obtain polyaluminum chloride through pyrolysis or neutralization.
The process flow of producing polyaluminum chloride from kaolin is roughly divided into three steps: roasting and activation of concentrate, acid leaching, and adjusting the alkalinity of acid leaching solution to generate polyaluminum chloride solution.
4. Crystalline aluminum chloride
The production of polyaluminum chloride from crystallized aluminum chloride generally uses the boiling pyrolysis process. After the crystallized aluminum chloride is heated to a certain temperature, it decomposes a certain amount of hydrogen chloride gas and moisture and turns into a powdery product, which is polychlorination. Aluminum monomer (also known as clinker).
When a certain amount of water is added to the clinker and stirred, it will solidify in a short time to form a resinous product, which is polyaluminum chloride.
