Abstract
In literature, neutral polyethylene oxide (PEO) flocculated fines at low shear rates, while with cofactor (CF) addition, the formed CF-PEO complex showed larger ability to bridge fines, producing flocs. In this work, some process factors were found having significant effects on fines flocculation. Increases in CF to PEO ratio at constant PEO enhanced the bridging bonds, causing increases in flocculation initial rate (efficiency), amplitude (floc size), and fastness (a decrease in characteristic time). On the other hand, an increase in stirring rate (shear rate) in flocculation vessel caused decreases in initial rate and amplitude, and an increase in the fastness. All runs showed transient flocculation; the amplitude increased with time, reached maximum at equilibrium, and then started to decrease showing deflocculation. In brief, the CF to PEO ratio and the shear rate were found important parameters in mill operation, having significant effects on flocculation efficiency, fastness, and floc size.
Highlights
Flocculation process requires retention aid systems of dual- or multi-components to retain colloids and fines
This transient behavior was reported in previous work [3] in flocculation processes with polyethylene oxide (PEO) alone enhanced by CF addition, where the transition behavior was ascribed to the instable PEO entanglement which dissociates with time
Increases in CF addition at constant PEO and in a moderate range of CF to PEO ratio caused increases in flocculation amplitude, rate and fastness, making these moderate ratios recommended for use in flocculation and retention processes
Summary
Flocculation process requires retention aid systems of dual- or multi-components to retain colloids and fines. Inassociation-induce polymer bridging, the negative charge CF segments adsorbed on PEO coils expand and stiffen PEO coils to larger size (δ) due to repulsion among CF segments on the coils, making the coils capable to bridge surfaces. This large coil of PEO with CF is a CF-PEO complex, working as a polyelectrolyte capable to overcome the electrostatic double layer thickness ( κ −1 ) with a thickness δ > κ −1 [8]. When PEO was used alone, the inducing polymer bridging
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