Polyaluminum chloride (PAC) is an excellent inorganic polymer flocculant. It was first developed in Japan and put into industrial production in the 1960s. It is a mature technology and market pin Flocculant with large amount. When used, PAC has the advantages of fast floc formation, good sedimentation performance, less alkalinity consumption in water, and strong adaptability to changes in water temperature, pH value, turbidity and content of agricultural production system. Since the 1970s, China has carried out research and development on polyaluminum chloride. In recent years, with the deepening of laboratory research, industrial production has developed rapidly. This paper discusses and discusses the production technology of polyaluminum chloride in China from the perspective of different raw materials for PAC production. In the field of polyaluminum chloride water treatment, flocculation is one of the older solid-liquid separation methods. Due to its wide applicability, simple process, low treatment cost and other characteristics, flocculation is still widely used in the treatment of drinking water, domestic sewage and industrial wastewater.
[Preparation technology of polyaluminum chloride]
Using aluminum chips, aluminum ash and aluminum slag as raw materials
1.1.1 One step acid dissolution method
Add hydrochloric acid and water in a certain proportion to a certain amount of aluminum ash, fully react at a certain temperature, and after several hours of aging, discharge the upper liquid to obtain polyaluminum chloride liquid product. Aluminum reaction is exothermic reaction. If the reaction conditions such as the concentration and amount of hydrochloric acid, water volume, dosing rate and sequence are well controlled, the heat released by aluminum reaction can be fully utilized, so that the reaction can reduce the dependence on external heating amount, or even react by self heating without external heating source, and control its salinity to be qualified. This method has the characteristics of fast reaction speed, less investment and equipment, simple process, convenient operation, high product basicity and alumina content, so it is widely used in China. However, the equipment is severely corroded by this process, and the product produced has more impurities, especially the heavy metal content is easy to exceed the standard, and the product quality is unstable. Ruan Fuchang and others? Using electrolysis Aluminium powder The analytical pure hydrochloric acid is used as raw material to prepare ultrapure polyaluminum chloride in the laboratory, which is said to be used for preparing polyaluminum chloride standard solution in the laboratory.
1.1.2 Alkali dissolving method
First, aluminum ash is reacted with sodium hydroxide to obtain sodium aluminate solution, and then the pH value is adjusted with hydrochloric acid to obtain polyaluminum chloride solution. The product produced by this method has good appearance and less water insoluble matter, but it has high sodium chloride content, high raw material consumption, low content of aluminum oxide in solution, and high industrial production cost
1.1.3 Neutralization method
In this method, hydrochloric acid and sodium hydroxide are used to react with aluminum ash to produce aluminum chloride and sodium aluminate respectively, and then the two solutions are mixed and neutralized to produce polyaluminum chloride liquid. The product produced by this method has less insoluble impurities, but the cost is high. Liu Chuntao and others first reacted with hydrochloric acid and aluminum foil, and then divided the obtained aluminum chloride into two parts. One part was adjusted to pH value of 6~6.5 with ammonia Aluminium hydroxide Then, another part of aluminum chloride is added to aluminum hydroxide for reaction to obtain polyaluminum chloride liquid product, which is dried to obtain solid product. It is said that the aluminum content and salinity of the product are very high.
1.1.4 Original Battery method
This process is an improved one-step process of acid dissolution of aluminum ash. According to the electrochemical principle, metal aluminum can react with hydrochloric acid to form a primary cell. At the bottom of the barrel shaped reaction chamber, a metal screen made of copper or stainless steel is placed as the negative comparison, and poured aluminum chips are used as the positive comparison, and hydrochloric acid is added to react to finally produce PAC. In this process, the bubbles generated in the reaction can be used to make the solution move directionally, instead of mechanical stirring, which greatly saves energy consumption.
Spray drying polyaluminium chloride [Chinese name] Spray drying polyaluminium chloride [English name], abbreviated as PAC
[Molecular formula] [AL2 (OH) LnCL6-n] m
[Technical standard] The product quality meets the national standard GB15892-2009 [Characteristics of spray drying polyaluminum chloride]
The characteristics of pressure spray drying are mainly determined by the working principle of pressure atomizer, which makes this drying system have its own characteristics. Since the products obtained by pressure spray drying are porous particles or hollow particles, the purpose of pressure spray drying is to obtain granular products, and the granular products obtained have excellent dust prevention performance and flow performance. Due to the large contact area between the product and water, the wettability is better than that of powder products, and the speed of purified water is significantly higher than that of powder products. The pressure spray dried products have unique characteristics, so they are highly praised by users.
Spray granulation is to atomize polyaluminum chloride into tiny particles when it is dried. This type of granule has good application performance. Polyaluminium chloride is a water-soluble substance with good thermal stability and high solubility. During the drying process, 40% - 50% solid content of polyaluminium chloride solution is introduced High pressure pump After being pressurized, it enters the atomizer in the dryer for atomization, and is dispersed into tiny droplets. After the droplets are dried, they can get granular products, so that drying and granulation can be completed at the same time.
