Application of Anionic Polyacrylamide (APAM) in Sugar Industry Clarification Processes 2026

Part I: Introduction

In the modern sugar industry, the clarification process is a critical step determining final sugar quality, yield, and production cost. The raw mixed juice obtained from milling contains not only sucrose but also a large amount of non-sugar impurities such as proteins, pectins, organic acids, starches, and pigments. The core purpose of clarification is to remove these non-sugars as much as possible, thereby increasing juice “purity.” This enables the production of more and purer white sugar during subsequent crystallization, while also reducing juice viscosity and color value, ensuring smooth crystallization, and facilitating the resourceful utilization of by-products like filter mud.

With growing consumer demand for high-quality white sugar and sugar mills’ continuous pursuit of production efficiency, efficient and environmentally friendly clarification aids are gaining more attention. The application of APAM in sugar industry has become an important technical means for many advanced sugar mills worldwide to optimize the clarification process. APAM (Anionic Polyacrylamide) is a water-soluble high molecular weight polymer that plays a key role in the clarification of cane or beet juice.

Part II: Mechanism of APAM and Clarification Method Analysis

2.1 The Core Role of APAM: Coagulant Aid and Bridging

During sugar processing, the non-sugar impurities in the mixed juice (such as proteins, pectins, cane wax, starches, and fine fibers) are mostly surface-charged and exist in a relatively stable colloidal dispersion state, resulting in extremely slow natural sedimentation.

In this process, APAM acts primarily as a coagulant aid. Its mechanism does not directly determine the final destination of the impurities. Instead, through the adsorption bridging effect of its long molecular chains, it connects and captures multiple fine colloidal or suspended particles into larger flocs. Simultaneously, the anionic groups (-COO⁻) on its molecular chain undergo charge neutralization with some positively charged impurities, further promoting aggregation. This efficient aggregation effect lays the foundation for subsequent high-efficiency solid-liquid separation.

2.2 The Primary Role of Flotation: Formation of Light Flocs

In practice, especially during cane juice clarification, the process predominantly uses flotation rather than sedimentation. The reason lies in the density composition of the flocs.

Cane juice contains a significant amount of substances with a density close to or even less than that of water, such as cane wax, cane fat, certain proteins, and some colloids. Under the bridging action of PAM, these light impurities are encapsulated into flocs, forming “light flocs” with a specific gravity lower than that of the juice. At this point, when a large number of fine air bubbles are introduced into the juice, these light flocs quickly attach to the bubbles and, due to strong buoyancy, rise rapidly to the surface, forming a scum that is easily removed, thus achieving efficient separation.

2.3 The Possibility of Sedimentation: Influence of High-Density Impurities

When auxiliary clarifying agents such as phosphoric acid and lime are added, heavier precipitates like calcium phosphate or calcium carbonate are formed. PAM can also adsorb these dense particles. When the resulting flocs have a specific gravity greater than that of the juice, they will settle to the bottom as mud. Therefore, PAM itself does not determine whether the flocs float or sink; rather, it enhances the separation process according to process requirements. In practice, an efficient approach often employs a combined “flotation + sedimentation” process: flotation is used first to remove light impurities like cane wax and proteins, followed by the sedimentation of the remaining mud or separation via a clarifier.

The typical reaction pathway can be summarized as:

Charged/Suspended Impurities + PAM (Coagulant Aid) → Adsorption Bridging & Charge Neutralization → Formation of Large Flocs

• If light impurities (e.g., cane wax) are encapsulated + Micro-bubbles → Flotation (Primary Method)
• If heavy precipitates (e.g., calcium phosphate/calcium carbonate) are encapsulated → Sedimentation (Auxiliary Method)

Part III: The Critical Role and Mechanism of pH Adjustment

Adjusting the pH value is a prerequisite for activating APAM performance and coordinating the entire clarification chemical system. Without proper pH adjustment, APAM may become completely ineffective or even counterproductive. Its importance is reflected in the following three aspects:

3.1 Ensuring Optimal APAM Molecular Conformation

APAM is a weak-acid type polyelectrolyte. The degree of ionization of the anionic groups on its molecular chain and the extended conformation of the chain are significantly affected by pH.

• Too Low pH (Strongly Acidic, pH < 4): Carboxylate groups combine with hydrogen ions (H⁺) to form non-ionized carboxyl groups (-COOH). The negative charge on the molecular chain decreases or disappears, causing the chain to curl from an extended state into a tight spherical shape. The bridging capacity of the curled APAM molecule drops sharply, resulting in very poor flocculation.
• Too High pH (Strongly Alkaline, pH > 10): Although the APAM molecular chain is fully extended, the strongly alkaline environment may cause hydrolysis of the amide groups or even degradation and breakage of the polymer chain, losing molecular weight and flocculation performance.
• Optimal pH Range (Weakly Acidic to Neutral/Slightly Alkaline, approximately pH 5.5 – 8.5): The anionic groups of APAM are fully ionized, and the molecular chain exhibits a fully extended linear structure due to mutual repulsion of negative charges. This maximizes its adsorption bridging capacity, effectively capturing and connecting suspended particles.

3.2 Modifying the Surface Charge of Impurity Particles

Non-sugar impurities (proteins, colloids, etc.) are mostly positively charged on their surfaces, while APAM is negatively charged, functioning through charge neutralization and adsorption bridging.

• The Zeta potential (surface charge intensity) of impurity particles varies with pH. By adjusting the pH, the surface charge characteristics of impurity particles can be optimized to generate the strongest electrostatic attraction with the negatively charged groups on the APAM molecular chain, promoting particle destabilization and aggregation from the colloidal state.

3.3 Optimizing Chemical Reactions of Auxiliary Clarifying Agents

Sugar clarification typically uses auxiliary clarifying agents such as lime, phosphoric acid, sulfur dioxide, or carbon dioxide in combination with APAM.

• Calcium Phosphate Precipitation: The reaction between phosphoric acid and lime produces calcium phosphate (Ca₃(PO₄)₂). This reaction is very sensitive to pH. Only when the pH is precisely controlled within the range of 7.0 – 7.5 (sulfitation process) or a slightly higher range can a flocculent, highly adsorptive calcium phosphate precipitate be formed, serving as the “core” for APAM bridging.
• Calcium Carbonate Precipitation: In the carbonation process, the pH needs to be controlled within the range of 10.0 – 11.0 (after first carbonation saturation) to generate fine, highly active calcium carbonate (CaCO₃) precipitates for adsorbing non-sugar impurities.
• Avoiding Scaling Issues: Improper pH can lead to the formation of insoluble calcium salts (such as calcium sulfate or calcium oxalate) or the re-stabilization of some colloids, increasing the risk of scaling in subsequent evaporators.

3.4 pH Control Ranges in Actual Production

Clarification Process	Typical pH Range (Before APAM Addition)	Purpose
Sulfitation (Cane)	7.0 – 7.5 (near neutral)	Generate optimal calcium phosphate precipitate; ensure APAM chain is fully extended; effectively remove light impurities (via flotation)
Carbonation (Cane/Beet)	10.0 – 11.0 (after first carbonation)	Generate highly active calcium carbonate precipitate; cause some pigments and colloids to dissolve or denature under alkaline conditions for easier adsorption and removal
Near-neutral/Weakly Alkaline	7.5 – 8.5	pH range for some modified processes or pre-liming in beet sugar mills; balances APAM effectiveness with equipment corrosion prevention

Core Logic Chain:

Part IV: Main Applications of APAM in Sugar Industry

4.1 Flotation/Clarification of Cane Juice

In sulfitation or carbonation sugar mills, APAM is typically added after the neutralized or first carbonation juice, before it enters the flotation or sedimentation unit, and it is critical to ensure the pH has been adjusted to the optimal range required by the process. The dosage is typically controlled at 1 – 5 ppm (based on raw juice volume). This low addition level can:

• Significantly improve clarified juice quality: Turbidity can be reduced to 30–50 mg/L, and color value reduced by over 15%.
• Increase production capacity: Flotation/sedimentation tank throughput increases by 15–30%.
• Reduce mud volume by 15%–25%, facilitating subsequent resource utilization (e.g., animal feed, organic fertilizer, cane wax extraction).

4.2 Clarification of Beet Juice

For beet sugar mills, where the colloid content is higher, APAM is also suitable for sedimentation processes including pre-limed, main limed, and first carbonation juice. Its flocculation effect helps improve filtration speed and filtrate purity.

4.3 Thickening and Filtration of Mud

The mud at the bottom of the sedimentation tank (containing considerable sugar) needs to be processed through vacuum drum filters or filter presses for sugar recovery. APAM can be used for mud pre-treatment, forming a denser filter cake structure, thereby improving filtration efficiency and reducing filter cake moisture content.

Part V: Key Advantages of APAM Application

Advantage Category	Specific Performance
Improved Clarified Juice Quality	Clarified juice turbidity reduced to 30–50 mg/L, color value reduced by >15%
Increased Production Capacity	Flotation/sedimentation tank throughput increased by 15–30%, easing equipment bottlenecks
Reduced Auxiliary Material Consumption	Allows moderate reduction in usage of conventional clarificants like lime and phosphoric acid
Reduced Scaling Issues	Higher clarified juice purity significantly slows scaling in evaporators and heaters, extending cleaning cycles
Improved Final Sugar Quality	Reduced color value and ash content in final sugar, higher white sugar grade
Environmental & Resource Benefits	Higher sugar recovery from mud, reduced COD load in wastewater; filter mud can be used for feed, fertilizer, or wax extraction

Part VI: Industrial Application Case Studies

Case 1: A Sulfitation Cane Sugar Mill (8,000 tons crushing capacity per day)

• Problem: With natural sedimentation alone, clarified juice turbidity fluctuated significantly (150–300 mg/L), with severe mud carryover in the overflow.
• Solution: Precisely controlled the neutralized juice pH to 7.0–7.5 and added 1.5–2.5 ppm APAM before it entered the flotation unit.
• Results:
  • Clarified juice turbidity stabilized below 40 mg/L, with virtually no visible mud in the overflow.
  • Filter cake sugar content reduced by approximately 1.5 percentage points, improving sugar extraction rate.
  • The scum (cane wax, proteins) was effectively separated, facilitating subsequent comprehensive utilization.

Case 2: A Carbonation Beet Sugar Mill

• Problem: Slow sedimentation of first carbonation juice and difficulty in mud filtration.
• Solution: Ensured the first carbonation juice pH was within 10.0–11.0 and added 2–3 ppm APAM.
• Results:
  • Sedimentation rate increased by 25%.
  • Filtration rate increased by 30%.
  • Filter cake moisture content reduced by 5%.

Part VII: Conclusion

The application of APAM in the sugar industry is a mature, efficient, and economical clarification technology. Its core role is as a coagulant aid, aggregating fine impurities into large flocs through adsorption bridging and charge neutralization. In cane juice clarification, due to the presence of light impurities such as cane wax and proteins, the resulting flocs have a specific gravity lower than the juice, making flotation the primary method for rapid separation. It can also assist in sedimentation when dense precipitates are formed.

However, there is a crucial prerequisite for APAM to perform effectively—precise pH adjustment. Only within the optimal pH range can the APAM molecular chain fully extend, the surface charge of impurities be optimized, the auxiliary clarifying agents form the optimal precipitate morphology, and efficient flocculation and solid-liquid separation be achieved.

For sugar mills seeking to significantly improve clarification performance without major equipment modifications, selecting the appropriate APAM specification, rigorously controlling and optimizing the pH, and optimizing the addition process based on the specific process (flotation or sedimentation) represents a technical upgrade with an extremely high return on investment. Furthermore, the separated filter mud can be used to produce animal feed, organic fertilizer, or extract cane wax, delivering both economic and environmental benefits.