Hydrate Flocculants

In plants that produce sandy (coarse) alumina, precipitation is followed by a hydrate classification circuit. The circuit serves to segregate coarse hydrate from finer hydrate, and is usually composed of primary, secondary, and tertiary classifiers operating in series. The coarse hydrate, from the primary classifier, is sent on to calcination while the finer hydrate is recirculated back to precipitation to be used as seed. In most instances, the classification circuit further segregates the seed into coarse and fine fractions. Underflow from the secondary classifiers is coarse seed, while underflow from the tertiary classifiers is fine seed. Overflow from the tertiary classifiers is spent liquor and is routed through evaporation and then to digestion. Flocculants play an important role in the operation of the tertiary classifiers, minimizing the amount of hydrate in the overflow. Hydrate in the overflow represents a recirculating load going back to digestion, and reduces the overall yield of the plant. Most plants generally try to control the concentration of hydrate in the tertiary overflow to one gram per liter or less.

The current products in commercial use are CYFLOC® HF 1110 and CYFLOC® 2220 (Table 4). As shown in the lab testing results (Figure 8), both products significantly improve the settling rates of alumina trihydrate, and reduce the overflow (O/F) solids. As shown in a plant trial (Table 5), the application of CYFLOC® HF 1110 in the tertiary thickener allowed the plant to handle higher feed solids while achieving lower overflow solids, as compared to incumbent.  In addition to the flocculation and settling capability, these products substantially improve the rheology of the settled alumina trihydrate when applied in the tertiary classifiers. As a result, the drainage time of the underflow solids can be significantly reduced (Figure 9).

Table 4. Syensqo Hydrate Flocculants

ProductFormPolymer TypeChargeMol. Wt.Application
CYFLOC® HF-1110Aqueous solution
Polysaccharide		Moderate
High		Hydrate flocculant
CYFLOC® HF-2220Aqueous solution
Polysaccharide		Moderate
High		Hydrate flocculant
The hydrate flocculation performance of CYFLOC® HF 1110 and HF 2220 in the lab testing.
Figure 8. The hydrate flocculation performance of CYFLOC® HF 1110 and HF 2220 in the lab testing.
The impacts of CYFLOC® HF 1110 and HF 2220 on the drainage time of hydrate underflow in the lab testing.
Figure 9. The impacts of CYFLOC® HF 1110 and HF 2220 on the drainage time of hydrate underflow in the lab testing.
Table 5. Plant trial result for application of CYFLOC® HF 1110 in the tertiary thickener.
 Pre-trialTrial
Incumbent flocculant dose (ppm)260
CYFLOC® HF 1110 dose (ppm)012
Feed solids (g/L)74100
Overflow solids (g/L)2.30.65

 

In addition to using these products in the tertiary classifiers, CYFLOC® HF 1110 and HF 2220 can also be added in secondaries or hydrate storage tanks with the following advantages:

  • Significantly improved underflow rheology
  • Improved control of the classification circuit
  • Reduced overflow solids
  • Increased seed charge density
  • Reduced recirculating load of fine hydrate in the classification circuit