lime softening silica removal

In lime softening, silica is removed by adsorption onto magnesium precipitates, which generally occur at higher pH (above 10.5, and often require addition of a magnesium source)2. Silica can exist in water as relatively large particles, known as silica granules or granular silicates. By applying this secondary treatment, an extra 9% boron removal and a 15% silica removal were achieved when softened groundwater was mixed with EMAG45 in a molar Mg/B ratio of 125. Warm Lime Softening. Though this paper only mentions about the role of magnesium hydroxide in removing silicate,  I wonder if some silicate will similarly adsorbed on to calcium hydroxide (lime) directly and be removed if calcium hydroxide is added in high enough concentrations. Lime softening utilizes the addition of lime (calcium hydroxide) to remove hardness (calcium carbonate and magnesium carbonate) ions by precipitation. Although no CO2 addition is mentioned in this paper, it gives us a clue for its role in the above mentioned experiments which started this whole discussion. Ionisation of soluble Si(OH)4 to silicate ions also increases with pH greater than 7. 59 0 obj<>stream ( Log Out /  Design Flow (mgd) 0.01. The effect of lime concentration on silica removal during softening was investigated. Chemicals normally used are lime (calcium hydroxide, Ca(OH) 2) and soda ash (sodium carbonate, Na 2CO 3). Fig. The solubilities of calcium, magnesium, and silica are reduced by increased temperature. Chemical precipitation is one of the more common methods used to soften water. But, we couldn’t get our heads around how lime addition was linked to silica removal (though we understood the silica was somehow precipitated out), and what purpose the CO2 addition served. Plants A, B, C and D use another method of clarification called lime softening. ( Log Out /  Magnesium hydroxide also removes silica via absorption as it precipitates. Hot Lime Softeners. In these experiments, CO2 was also dosed in conjunction with lime. 2. During lime softening, calcium bicarbonate is precipitated out as calcium carbonate. Since 1976, Ecodyne has supplied hot lime softeners for the removal of hardness, alkalinity, turbidity, oxygen, silica removal and other contaminants in OTSGs and boilers. Lime softening, in particular, is the removal of Ca and Mg ions through the addition of  addition of lime, Ca(OH)­2. Enhanced softening is the removal of natural organic matter (NOM) during precipitative softening, with an objective of reducing the formation of disinfection by‐products (DBPs). Current silica removal processes in industrial water treatment rely heavily on: • Lime-softening style silica precipitation , which has a large footprint, creates large volumes of sludge, is difficult to operate and subject to upsets, and has a high capital cost; and 0000002406 00000 n Lime Softening Lime softening has been widely used in industrial applications, primarily for cooling tower and boiler feed applications. 0000000855 00000 n Hot Lime Softening can be used to mitigate these The soluble silica cannot be removed by filtration. Measurements of silica content of softened water will be performed at different pH level in the precipitator. However, magnesium carbonate is a soluble salt! Also included is on-site erection and pre-assembly, depending on the location and site access. Before we discuss what might be the best method of removing silica, let's talk about what silica is. There are various ways to remove silica from a water supply, including lime softening, ion exchange, reverse osmosis, ultrafiltration, and electrocoagulation. 0000002158 00000 n startxref Effective use of coagulants helps remove silica in the softening process. It has been known for many years that silica removal during soda-lime softening is dependent on the precipitation of dissolved magnesium present in water by conversion to Mg(its OH) 2. at a pH above 10.2. 0 The soluble silica is generally removed by the method of precipitation with other salts. The solubilities of calcium, magnesium, and silica are reduced by increased temperature. These solids … 3.1 Influent Cold Lime Softening . Graver customizes our Reactivator Clarifier design to accommodate cold lime or warm lime operation as required for TSS hardness, alkalinity and silica removal. the complex issue of silica removal as a pretreatment step to RO. Silica is generally present in … Approximate Costs of Lime Softening. We have several unique features in our hot lime softeners. Granular silica removal is generally accomplished through physical chemical separation. Conventional lime softening is the traditional water softening process for high volume flows, and involves adding lime [Ca(OH)2] and soda ash (Na2CO3). Therefore, they are more effectively removed by warm lime softening than by cold lime softening. ( Log Out /  In lime softening the silica is co-precipitated along with magnesium present in the water (or added if necessary). Magnesium oxide has been found to quite effective in this regards. Measurements of silica content of softened water will be performed at different pH level in the precipitator. But, then again, adding excess lime may not be the ideal solution as it will increase the hardness of water (which we were trying to reduce in the first place)? Change ), You are commenting using your Facebook account. Interestingly, silica (SiO2), a major constituent of concern for RO membrane fouling,  can also be removed through the series of precipitation reactions that occur with lime addition. The problem with the lime softening method is that it can be quite costly. WARM LIME SOFTENING The warm lime softening process operates in the temperature range of 120-140°F (49-60°C). Silica tends to be absorbed in the floc produced by coagulation of sludge. As sodium carbonate will not be precipitated out, it will add to the scaling potential of any downstream RO processes. 0000000935 00000 n This process is used for the following purposes: Therefore, they are more effectively removed by warm lime softening than by cold lime softening. All these problems make the silica removal from your drinking water a tough process. Upon precipitation, magnesium hydroxide forms larger flocs which entraps and adsorbs in soluble silica particles in water. 48 0 obj <> endobj Lime softening can also be used to remove iron, manganese, radium and arsenic from water. It will be apparent, therefore, that my silica removal treatment is well suited for use in conjunction with the hot lime soda process of softening hard water. �,G⮷�^ɓ�����b,Ը=� 0000002672 00000 n 10 shows silica and boron removal (%) combining the lime and soda ash softening treatment followed by polishing treatment by means of adsorption with EMAG45. 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. Softening refers to the process of removing hardness ions such as Ca and Mg from water. This article will discuss lime softening through a new perspective, instead of going through the detailed chemical equations; we will focus on “practical conclusion” of the reactions. endstream endobj 49 0 obj<> endobj 50 0 obj<> endobj 51 0 obj<>/ProcSet[/PDF/Text]/ExtGState<>>> endobj 52 0 obj<> endobj 53 0 obj<> endobj 54 0 obj<> endobj 55 0 obj<> endobj 56 0 obj<> endobj 57 0 obj<>stream Silica is removed by adsorption on the magnesium precipitates. 0000001602 00000 n The unique features of our lime softeners allow this equipment to treat the hot produced water in the SAGD process. The removal … Lime softening. 0000002748 00000 n Warm Lime Softening Process: The warm lime softening process operates in the temperature range of 120-140°F (49-60°C). Ph is increased from the lime addition, calcium bicarbonate is converted to magnesium carbonate ) ions precipitation... Soften the water hydroxide ) to remove manganese, fluoride, organic and! 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