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Clarification - Refining

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By Bento, Luis San Miguel
Posted on 2006-09-18    Last edited on 2010-12-08

 

Raw sugar contains non-soluble solid matter (bagacillo, sand, colloidal matter) that are not separated during Affination. Therefore, affination liquor has high turbidity, and a clarification process is needed, before the Decolourization step. The removal of suspended solids is important, as affinaton liquor will be treated with adsorbent carbons or ion exchange resins,  high porosity adsorbents. The presence of fine particles of suspended solids in the liquor will provoke the blockage of the pores of these materials, decreasing their decolourization capacity. Also, suspended matter can be occluded in white sugar crystals during crystallization, affecting sugar quality. Therefore, the suspended solids must be removed from affination liquor, before Decolourization and Crystallization.

Liquor clarification can be done in different ways, being the more usuals:

- filtration with diathomacea earths;
- carbonatation;
- phosphatation.

The first of the mentioned processes consist in addition to the affined liquor a filter aid, normally, a medium grade diathomacea earth (type High Flow Supercel), in a quantity between 0,3% and 0,5%, on solids. This mixture is filtered in rotative , plate and frame or membrane pressure filters. In these filters a pre-coat is made with filter aid.

In Carbonatation and Phosphatation processes, calcium carbonate or phosphate precipitate, respectively, is formed. This precipitate will co-precipitate some high molecular material and suspended solids will be removed jointly with it. The presence of calcium at the precipitate surface can fixe anionic colourants that will be removed from liquor. In phosphatation it is usual to use a cati0nic polymer that will remove colourants from solution.

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