Examination of Silica Removal with Solids Recycle for Reverse Osmosis Pretreatment
type: CreativeWork
description: Water treatment methods serve to remove harmful constituents from ground and surface waters prior to municipal distribution by exploiting the physical and chemical properties of those constituents. Properties can include size, charge, or solubility. Silica (SiO2) is difficult to remove during water treatment because it can exist in ground and surface waters as various dissolved and particulate species, all of which are defined by different properties. Silica speciation is dependent on variables like pH, temperature, concentration, and ionic composition. Consumption of silica as it exists in drinking water is not dangerous to humans or animals, but it can form damaging scales on the surfaces of industrial equipment and reverse osmosis membranes. For this reason, the subject of silica removal has been the focus of many studies; yet, there remains much to be learned. This thesis aimed to study the complex issue of silica removal as a pretreatment step to RO. A review of the literature indicated that silica is most commonly removed during a lime softening process but that removal is tied mostly to the presence of magnesium. Furthermore, studies have shown that removal is best when the chemical softening process is operated at a pH of 10 or above. Magnesium hydroxide precipitates in this higher pH range thereby removing silica via a co-precipitation or adsorption mechanism. This project explored the relationship between magnesium concentration, pH, and silica removal in two phases. Phase 1 included 21 jar tests that studied silica removal within a pH range of 7 to 12 and with different concentrations of dissolved magnesium chloride (MgCl2) and freshly precipitated magnesium hydroxide (Mg(OH)2); freshly precipitated ferric hydroxide (Fe(OH)3) was also studied in one test. Phase 2 flow-through experimentation consisted of 5 tests that were conducted in a system operating around a pH of 9.5 or 10 with solids recirculation. Mg(OH)2 and Fe(OH)2 were tested in Phase 2. The con…
abstract: Water treatment methods serve to remove harmful constituents from ground and surface waters prior to municipal distribution by exploiting the physical and chemical properties of those constituents. Properties can include size, charge, or solubility. Silica (SiO2) is difficult to remove during water treatment because it can exist in ground and surface waters as various dissolved and particulate species, all of which are defined by different properties. Silica speciation is dependent on variables like pH, temperature, concentration, and ionic composition. Consumption of silica as it exists in drinking water is not dangerous to humans or animals, but it can form damaging scales on the surfaces of industrial equipment and reverse osmosis membranes. For this reason, the subject of silica removal has been the focus of many studies; yet, there remains much to be learned. This thesis aimed to study the complex issue of silica removal as a pretreatment step to RO. A review of the literature indicated that silica is most commonly removed during a lime softening process but that removal is tied mostly to the presence of magnesium. Furthermore, studies have shown that removal is best when the chemical softening process is operated at a pH of 10 or above. Magnesium hydroxide precipitates in this higher pH range thereby removing silica via a co-precipitation or adsorption mechanism. This project explored the relationship between magnesium concentration, pH, and silica removal in two phases. Phase 1 included 21 jar tests that studied silica removal within a pH range of 7 to 12 and with different concentrations of dissolved magnesium chloride (MgCl2) and freshly precipitated magnesium hydroxide (Mg(OH)2); freshly precipitated ferric hydroxide (Fe(OH)3) was also studied in one test. Phase 2 flow-through experimentation consisted of 5 tests that were conducted in a system operating around a pH of 9.5 or 10 with solids recirculation. Mg(OH)2 and Fe(OH)2 were tested in Phase 2. The con…
author: Sims, Magdalena
language: English
keywords: silica removal, reverse osmosis pretreatment, silica scale, membrane fouling, solids recycle, adsorption, co-precipitation, magnesium hydroxide, flow-through experimentation, solids recirculation
date published: 2015-09-01T07:00:00Z
date modified: 2026-07-24T05:26:55Z
provider: University of New Mexico
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of New Mexico

PropertyValue
property ID: Handle
value: http://hdl.handle.net/1928/30362