Polyaluminium chloride: Properties, applications and development prospects

Abstract

Polyaluminum Chloride (PAC) is a commonly used inorganic polymer flocculant, widely used in drinking water treatment, sewage treatment, paper making, petroleum industry and other fields. In this paper, the properties, preparation methods, main uses and application status in various fields of polyaluminum chloride are introduced in detail, and its development trend and future prospect are discussed.

1. Introduction

Water treatment is one of the important environmental protection issues facing the world. With the acceleration of industrialization and urbanization, the problem of water pollution is becoming more and more serious. As an indispensable part of the water treatment process, flocculant plays a key role. As a kind of efficient flocculant, polyaluminum chloride has been widely used and paid attention to because of its excellent performance. In this paper, the characteristics, application and development prospect of polyaluminum chloride are introduced.

2. Properties of polyaluminium chloride

2.1 Chemical structure

Polyaluminum chloride is a kind of inorganic polymer compound, its molecular formula can be expressed as [\text{[Al_2(OH)_nCl_6-n]_m} ], where [1 \leq n \leq 5 ], [m ] indicates the degree of polymerization. It is formed by multiple aluminum ions connected by hydrogen-oxygen Bridges and chlorine Bridges.

2.2 Physical properties

• ** Appearance ** : Polyaluminum chloride is usually yellow, light yellow or dark brown powder or particle, also in liquid form.
• ** Solubility ** : easily soluble in water, forming a colloidal solution with strong water absorption.
• ** Density ** : about 1.15-1.20 g/cm³ (liquid), solid density varies by product.
• **pH ** : The pH of an aqueous solution is usually between 3.5-5.0.

2.3 Chemical properties

Polyaluminum chloride has strong flocculation and adsorption, and can effectively remove suspended matter, colloid, bacteria, organic matter and metal ions and other pollutants in water. At the same time, the flocculation performance of PAC is less affected by pH value, and the application range is wide.

3. Preparation method of polyaluminum chloride

3.1 Neutralization method

Neutralization is one of the most common preparation methods. Polyaluminium chloride is formed by reacting aluminium hydroxide with hydrochloric acid:

[ \text{Al(OH)_3 + 3HCl → AlCl_3 + 3H_2O} ]

Then the reaction conditions were further controlled to make the generated aluminum chloride partially hydrolyzed and polymerized to form polyaluminum chloride.

3.2 Addition method

The addition method is to directly add aluminum powder into concentrated hydrochloric acid, and by controlling the reaction temperature and time, the aluminum powder reacts with hydrochloric acid to form polyaluminum chloride:

[ \text{Al + HCl → AlCl_3} ]

During the reaction, polymeric aluminum chloride with high molecular weight was produced by adding stabilizer and controlling hydrolysis conditions.

3.3 Alkalization process

The alkalization method is to mix the aluminum chloride solution with the sodium hydroxide solution, and by controlling the alkalization degree and reaction conditions, the aluminum chloride is partially hydrolyzed to form polyaluminum chloride:

[ \text{AlCl_3 + NaOH → Al(OH)nCl{3-n} + NaCl} ]

The method can control the degree of polymerization and performance of the product by adjusting the degree of alkalinity.

4. Main uses of polyaluminium chloride

4.1 Drinking water treatment

The main function of polyaluminum chloride in drinking water treatment is to remove suspended matter, colloid and organic matter in water. It has the advantages of fast flocculation speed, compactness of the formed floc and fast settling speed, which can significantly improve water quality and reduce turbidity.

4.2 Sewage treatment

In the field of sewage treatment, polyaluminum chloride is often used to remove pollutants such as organic matter, heavy metal ions and phosphate in sewage. Due to its good flocculation performance, it can effectively reduce the chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of sewage, and improve the efficiency of sewage treatment.

4.3 Paper industry

In the paper industry, as a retention agent and filter aid, polyaluminum chloride can improve the retention rate and water filtration performance of pulp, reduce the loss of fibers and fillers, and improve the quality and production efficiency of paper.

4.4 Petroleum industry

Polyaluminum chloride is often used in oil field water injection treatment, its main function is to remove suspended matter and organic matter in water injection, prevent water injection system blockage, and improve water injection efficiency.

4.5 Other fields

Polyaluminum chloride is also widely used in printing and dyeing, leather, chemical and other industrial wastewater treatment, as well as in medicine, cosmetics and other fields of application.

5. Examples of application of polyaluminum chloride in various fields

5.1 Application examples in drinking water treatment

Xi ‘an Drinking Water Plant uses polyaluminum chloride for water treatment. By adjusting the dosage and coagulation time, the turbidity and organic content of raw water are significantly reduced, and the water quality is improved, reaching the national drinking water standard.

5.2 Application examples in sewage treatment

The wastewater treatment station of Xianyang Chemical Plant uses polyaluminum chloride to treat wastewater. By adjusting the dosage of flocculant and reaction time, the suspended matter and heavy metal ions in wastewater are effectively removed, so that the wastewater after treatment can meet the discharge standard.

5.3 Application examples in paper industry

By optimizing the process parameters, the paper pulp retention rate and water filtration performance were improved, the loss of fiber and filler was reduced, and the paper quality and production efficiency were improved in Weinan Paper Mill.

5.4 Application examples in petroleum industry

By controlling the dosage and reaction time, the suspended matter and organic matter in the water injection were removed, the blockage of the water injection system was prevented, and the water injection efficiency was improved.

6. Research progress of polyaluminium chloride

With the increasing demand of water treatment, the research of polyaluminum chloride is also deepening. The main research areas include:

1. ** Improve the preparation process ** : By optimizing the preparation process of polyaluminum chloride, improve its stability and flocculation effect.
2. ** Composite flocculant ** : The composite use of polyaluminum chloride with other flocculants to further improve its treatment effect.
3. ** Application expansion ** : Explore the application of polyaluminum chloride in different water quality and different treatment conditions to expand its scope of application.
4. ** Environmental Impact Assessment ** : Study the environmental impact and ecological toxicity of polyaluminum chloride to ensure its safety during use.

7. Market and prospect of polyaluminum chloride

7.1 Market demand

With the increasing shortage of global water resources and the problem of water pollution, the demand of water treatment market is increasing. As a kind of high efficiency flocculant, polyaluminum chloride has a broad application prospect in drinking water treatment and sewage treatment.

7.2 Competitive advantage

Compared with traditional flocculants, polyaluminum chloride has the advantages of less dosage, better flocculation effect, wide application range, etc., and strong market competitiveness. In the future, with the improvement of the preparation process and the development of new products, the application range of polyaluminum chloride will be further expanded.

7.3 Development direction

In the future, the development of polyaluminum chloride will move in the direction of high efficiency, environmental protection and low cost. Through the introduction of new materials and new technologies, the development of new polyaluminum chloride products with higher flocculation performance and lower environmental impact will become the focus of research and industrialization.

8. Conclusion

As an efficient inorganic polymer flocculant, polyaluminum chloride is widely used in drinking water treatment, sewage treatment, paper making, petroleum industry and other fields due to its excellent flocculation and precipitation ability. Through reasonable use method and scientific dosage control, polyaluminum chloride can significantly improve the efficiency and effect of water treatment, and achieve the dual purpose of cost saving and environmental protection. The future,