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Silica removal in industrial effluents with high silica content and low hardness

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Latour, Isabel and Miranda, Rubén and Blanco, Ángeles (2014) Silica removal in industrial effluents with high silica content and low hardness. Environmental Science and Pollution Research, 21 (16). pp. 9832-9842. ISSN 0944-1344 (Print) 1614-7499 (Online)

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Official URL: http://link.springer.com/article/10.1007/s11356-014-2906-8



Abstract

High silica content of paper mill effluents is limiting their regeneration and reuse after membrane treatments such as reverse osmosis (RO). Silica removal during softening processes is a common treatment; however, the effluent from the paper mill studied has a low hardness content which makes necessary the addition of magnesium compounds to increase silica removal. Two soluble magnesium compounds (MgCl2∙6H2O and MgSO4∙7H2O) were tested at five dosages (250-1500 mg/L) and different initial pHs. High removal rates (80-90%) were obtained with both products at the highest pH tested (11.5). With these removal efficiencies, it is possible to work at high RO recoveries (75-85%) without silica scaling. Although pH regulation significantly increased the conductivity of the waters (at pH 11.5 from 2.1 mS/cm to 3.7-4.0 mS/cm), this could be partially solved by using Ca(OH)2 instead of NaOH as pH regulator (final conductivity around 3.0 mS/cm). Maximum chemical oxygen demand (COD) removal obtained with caustic soda was lower than with lime (15% vs. 30%). Additionally, the combined use of a polyaluminum coagulant during the softening process was studied; the coagulant, however, did not significantly improve silica removal, obtaining a maximum increase of only 10%.


Item Type:Article
Uncontrolled Keywords:Silica removal, Magnesium, Softening, Co-precipitation, Membranes fouling, Effluent reuse, Paper recycling
Subjects:Sciences > Chemistry > Paper industry
Sciences > Chemistry > Chemical engineering
Sciences > Chemistry > Waste products
ID Code:29263
Deposited On:23 Mar 2015 12:39
Last Modified:01 Sep 2015 23:01

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