I. Introduction

In modern industrial production and urban development, water treatment technology plays a crucial role. As one of the core chemicals in the water treatment field, industrial-grade Polyaluminium Chloride (PAC for short) has become an indispensable chemical agent in industrial water supply, wastewater treatment, circulating water systems and urban sewage purification, etc., due to its outstanding flocculation performance, wide applicability and relatively environmentally friendly characteristics. This article will comprehensively explore the characteristics, mechanism of action and application practices in various fields of industrial-grade polyaluminium chloride.

Ii. Overview of Industrial-grade Polyaluminium Chloride

1.Basic characteristics

Industrial grade polyaluminium chloride is an inorganic polymer flocculant with the chemical formula [Al₂(OH)ₙCl₆ ₙ ₙ]ₘ, where n is 1-5 and m≤10. Compared with traditional aluminium salt coagulants, PAC has the following significant characteristics:

●High-efficiency flocculation capacity: dual effects of charge neutralization and adsorption bridging

●Wide pH adaptability range: The suitable pH range is 5-9 (6.5-7.5 for traditional aluminum salts)

●Fast sedimentation speed: The formed flocs are large and dense, and the sedimentation speed is 2 to 4 times faster than that of traditional aluminum salts

●Low residual aluminum content: The aluminum ion concentration in the effluent is usually lower than 0.1mg/L

●Low corrosiveness: Its corrosiveness to processing equipment is lower than that of other aluminum salts and iron salts

2. Production process

Industrial-grade PAC is mainly produced through the following processes:

●Calcium aluminate method: Bauxite + hydrochloric acid + calcium aluminate → Reaction → Maturation → finished product

●Aluminum hydroxide method: Aluminum hydroxide + hydrochloric acid → reaction → maturation → finished product

●Aluminum dross acid dissolution method: It is produced by using aluminum processing waste, with low cost but large quality fluctuations

Industrial-grade products are usually light yellow to reddish-brown liquids or solids, with an alumina (Al₂O₃) content ranging from 28% to 30%, and a basicity degree within the range of 60% to 85%.

Iii. In-depth Analysis of the Mechanism of Action

1.Electro-neutralization effect

PAC hydrolyzes in water to form various high-valent complex ions, such as [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺. These positively charged polymers can effectively neutralize the negative charges on the surface of colloidal particles, compress the double electric layer, reduce the ζ potential, and destabilize the colloid.

2.Adsorption bridging effect

The long-chain polymer structure of PAC can "bridge" and connect particles, forming a network structure. It captures suspended particles through van der Waals forces, hydrogen bonds and other actions, forming large and dense flocs.

3.The function of net capture and sweeping

When the dosage of PAC is large enough, the formed aluminum hydroxide precipitate can capture and sweep the tiny particles in the water during the sedimentation process and sink together.

Iv. Practical Application of Industrial Water Treatment

1.Industrial water supply treatment

In the process water preparation of industries such as power, chemical engineering, and electronics, PAC shows significant advantages:

●Turbidity removal effect: It has an excellent treatment effect on low-turbidity water (≤10NTU), and the turbidity of the effluent can be reduced to below 0.5NTU

●Organic matter removal: It can remove 30% to 60% of dissolved organic matter, reducing the load on subsequent treatment

2. Industrial wastewater treatment

●Printing and dyeing wastewater

●Electroplating wastewater

● Papermaking wastewater

3. Industrial circulating water system

In the circulating cooling water systems of industries such as steel and petrochemical, the application of PAC brings multiple benefits:

●Turbidity control: Maintain the turbidity of the circulating water below 5NTU

●Microbial control: Reduce the amount of biofilm by 30%-50%

●Corrosion inhibition effect: It forms a protective film on the metal surface, reducing the corrosion rate by 40%

●Chemical synergistic effect: It has a good synergistic effect with organophosphorus-based scale inhibitors

4. Urban sewage purification

In municipal sewage treatment plants, the application scenarios of PAC include:

●Primary enhanced treatment: Direct addition, the SS removal rate can reach 85%-95%

●Chemical phosphorus removal: Reacts with orthophosphate to form AlPO₄ precipitate, with a phosphorus removal efficiency of over 90%

●Sludge conditioning: Improve the dewatering performance of sludge and reduce the moisture content of the filter cake by 2% to 5%

●Emergency response: Respond quickly to sudden pollution incidents

V. Key Points of Application Technology

1.Optimization of the addition method

●Multi-point dosing: For complex water quality, 2 to 3 dosing points can be adopted

●Gradient increase method: Add 60% of the dose first, and add the remaining 40% at intervals of 2 to 3 minutes

●Online mixing: Use a static mixer or mechanical stirring, and control the G value at 300-500s⁻¹

2.Key points of parameter control

●pH adjustment: The optimal range is 6-8. If it exceeds this range, acid/alkali adjustment is required

●Temperature influence: When the temperature is below 5℃, the dosage should be increased by 20%-30% or the flocculation time should be prolonged

●Stirring intensity: Initial rapid mixing (100-200 RPM,1 minute), followed by slow flocculation (20-40 RPM,15 minutes)

3.Product Selection Guide

Select the appropriate specification according to the processing object:

●High basicity PAC(70%-85%) : Suitable for low-temperature and low-turbidity water and high-color wastewater

●Medium basicity PAC(50%-70%) : Preferred for conventional water quality, with a wide range of applications

●Low basicity PAC(30%-50%) : Suitable for high turbidity water and oily wastewater

Vi. Development Trends and Innovations

1.Product upgrade direction

●Composite PAC: Incorporates components such as iron, silicon, and calcium, such as polyaluminium ferric chloride (PAFC)

●Specialized PAC: A customized product developed for wastewater from specific industries

●High-purity PAC: Al₂O₃ content >30%, with extremely low heavy metal content, is used in high-end fields

2.Technological innovation

●Magnetic enhanced PAC: Loaded with magnetic particles, it can rapidly separate flocs through magnetic separation

●Photocatalytic PAC: Combined with photocatalysts such as TiO₂, it has both flocculation and degradation functions

●Biological PAC: Combined with microbial preparations, it simultaneously achieves physicochemical and biological treatment

3.Green manufacturing

●Raw material substitution: More secondary resources such as industrial waste aluminum and coal gangue are adopted

●Process optimization: Reduce energy consumption and minimize the discharge of "three wastes"

●Life cycle assessment: Optimizing product environmental performance from a full life cycle perspective

Vii. Conclusions and Prospects

Industrial-grade polyaluminium chloride, with its outstanding technical performance and significant economic and environmental benefits, has become a pillar product in modern water treatment technology. With increasingly strict environmental protection requirements and the growing pressure of water shortage, PAC technology will continue to innovate and develop:

●Expansion of application fields: Penetration into new areas such as rainwater treatment, black and odorous water body governance, and emergency water treatment

●Intelligent application: Deeply integrated with online monitoring and automatic control systems to achieve precise dosing

●Green development: Enhancing the green level of the entire chain from raw materials, production to application

●Globalization Layout: China's PAC technology Standards and Products Accelerate their "going global"

In the future, industrial-grade polyaluminium chloride will continue to play a core role in the water treatment field, providing solid technical support for the sustainable development of industry and the improvement of urban water environment. Enterprises should enhance technological innovation, develop more efficient, specialized and environmentally friendly series of products to meet diverse water treatment demands and make greater contributions to ecological civilization construction.