1. Role of Anionic Polyacrylamide (APAM) in Red Mud Washing

General Function in Alumina Refining
Anionic polyacrylamide is a widely used synthetic, water-soluble polymer with negatively charged functional groups—it serves as a flocculant that enhances flocculation, settling, and separation of fine particles. Its application improves filtration efficiency and reduces solid carryover, contributing to clearer overflow and better underflow clarification in alumina production processes chinafloc.comgosingletrack.com.

Alclar Flocculants Series
The Alclar family of flocculants, designed specifically for the Bayer process, targets several stages including:

• Clarification: betters the separation of red mud from Bayer liquor

• Red Mud Washing: accelerates red mud settling and produces clearer overflow liquor

• Hydrate Thickening and Liquor Clarification: improves process efficiency and crystal concentration solenis.com+2solenis.com+2.

2. Specific Insight: Alclar HP21

Product Background
Alclar HP21 is part of BASF’s—and now Solenis’s—Alclar line of powder flocculants for mineral processing, particularly alumina refining ImimgRedalyc.org.

Performance Advantages (Study Highlights)
An industry study (published in HOLOS, Brazil) evaluated powder flocculants from the Alclar line—including HP21, HP22, 662, and 3000. Key outcomes:

• Higher settling velocity: Powder flocculants (like HP21) showed faster red mud sedimentation.

• Greater underflow compaction: Higher density of settled solids, critical for recovery and reducing waste.

• Lower overflow turbidity: Clearer liquid is discharged after settling.

• Cost efficiency: Powder forms (Alclar® line) can be up to 70% cheaper than similar emulsion-based flocculants.

• Synergistic benefits: When combined with hydroxamate (a costly additive), powder flocculants reduce hydroxamate usage—further lowering costs Redalyc.orgwww2.ifrn.edu.br.

Summary: Application of Alclar HP21 in Red Mud Washing

Final Takeaway

Alclar HP21 is a high-performance, powder-form anionic polyacrylamide flocculant used in the red mud washing stage of the Bayer process. Its principal benefits are improved settling and separation, enhanced clarity, and cost efficiency compared to emulsion counterparts—making it a highly effective tool in alumina refinery operations.