Silica removal to prevent silica scaling in reverse osmosis membranes

Cob, S. Salvador; Hofs, B.; Maffezzoni, Carlo; Adamus, Jan; Siegers, W.G.; Cornelissen, Emile; Güner, Fatma Elif Genceli; Witkamp, G.J.

doi:10.1016/j.desal.2014.03.020

Cited by 52 publications

(14 citation statements)

References 19 publications

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“…Importantly, once silica scale is formed on the membrane surface, it is extremely difficult to remove by common procedures such as acid wash [1,7]. Silica precipitation and scaling can be alleviated by using commercial antiscalants [8,9], or by reducing silica concentration in the feed water by alumina adsorbents [10], electrocoagulation [2], or softening through a coagulation [11]. However, such pretreatments increase operational costs and can induce organic fouling and biofouling and thus various alternative approaches have been tested to deal with silica scaling.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, it was found that mineral scaling [15] and membrane surface functional groups [16,17] due to organic fouling affect the extent and properties of colloidal fouling on RO and nanofiltration (NF) membranes. The process of colloidal fouling appears mostly to be controlled by the competition of the permeation drag force due to permeation flux and the electric double layer repulsion potential between colloid and membrane [8][9][10]. Another issue of membrane fouling is membrane surface roughness effecting enhanced colloidal fouling [3,11,12].…”

Section: Introductionmentioning

confidence: 99%

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Silica Fouling in Reverse Osmosis Systems–Operando Small-Angle Neutron Scattering Studies

et al. 2021

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We present operando small-angle neutron scattering (SANS) experiments on silica fouling at two reverse osmose (RO) membranes under almost realistic conditions of practiced RO desalination technique. To its realization, two cells were designed for pressure fields and tangential feed cross-flows up to 50 bar and 36 L/h, one cell equipped with the membrane and the other one as an empty cell to measure the feed solution in parallel far from the membrane. We studied several aqueous silica dispersions combining the parameters of colloidal radius, volume fraction, and ionic strength. A relevant result is the observation of Bragg diffraction as part of the SANS scattering pattern, representing a crystalline cake layer of simple cubic lattice structure. Other relevant parameters are silica colloidal size and volume fraction far from and above the membrane, as well as the lattice parameter of the silica cake layer, its volume fraction, thickness, and porosity in comparison with the corresponding permeate flux. The experiments show that the formation of cake layer depends to a large extent on colloidal size, ionic strength and cross-flow. Cake layer formation proved to be a reversible process, which could be dissolved at larger cross-flow. Only in one case we observed an irreversible cake layer formation showing the characteristics of an unstable phase transition. We likewise observed enhanced silica concentration and/or cake formation above the membrane, giving indication of a first order liquid–solid phase transformation.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Silica Fouling in Reverse Osmosis Systems–Operando Small-Angle Neutron Scattering Studies

et al. 2021

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“…The equilibrium concentration of dissolved silica depends on the temperature, pH and chloride ion concentration in a solution [11], and silica scale is sometimes diminished by avoiding supersaturation or by adding chemical inhibitors [12,13]. Al(OH) 3 [14], magnesium salt [15,16], silica gel seeds [17] and other chemicals [18,19] have also been used to induce the precipitation of silica. In addition, Gabelich et al [20] reported that increasing the pH of an ionic solution effectively induces the precipitation of silica, with significant removal of silica above a pH of 10.…”

Section: Introductionmentioning

confidence: 99%

Preventing Silica Scale Formation Using Hydroxide Ions Generated by Water Electrolysis

Sano

Yamaguchi

2019

Membranes

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The reaction of silica with various cations in a solution and with hydroxide ions generated by water electrolysis was investigated as a means of preventing the formation of silica scales in geothermal binary power generation. Through batch and continuous experiments, it was found that all silica in the cathode phase of a reaction device could be removed if the necessary amounts of magnesium and calcium were present. This occurs because a silica-magnesium-calcium compound is produced via a polymerization reaction with cations in a solution and with hydroxide ions generated by electrolysis. Analysis by inductively coupled plasma and energy dispersive X-ray spectroscopy shows that this material has the formula 2CaO-5MgO-8SiO2-H2O, and thus is likely generated by the reaction proposed by Sheikholeslami et al. (2019). Increasing the current sent through the reaction solution subsequently produces calcium carbonate. This technique for the separation of silica and calcium from aqueous solutions can be operated continuously without channel clogging, which indicates the possibility of practical applications. However, overly high currents promote the migration of protons from the anode to cathode phases, which inhibits the formation of precipitates due to a neutralization reaction. The proposed method is an effective approach for removing silica from a solution in geothermal binary power generation; although, a means of suppressing the effects of proton generation will be necessary if the process is also to be used to remove calcium ions.

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“…Thus, coagulation processes are the best treatment option for removing silica from HERO concentrate solutions. Several previous studies have found that dissolved silica can be removed from solution using either chemical coagulation or electrocoagulation (EC) using Fe 3+ or Al 3+ ions [9,10,11,12,13,14,15,16]. Because Al 3+ coagulation processes are less effective at pH values greater than 8, coagulation processes based on Fe 3+ are preferred in high pH solutions [17].…”

Section: Introductionmentioning

confidence: 99%

Evaluating electrocoagulation and chemical coagulation for removing dissolved silica from high efficiency reverse osmosis (HERO) concentrate solutions

Chen

Baygents

2017

Journal of Water Process Engineering

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High efficiency reverse osmosis (HERO) produces high pH concentrate streams that often contain high levels of dissolved silica. Removal of silica from these concentrate streams is desirable before brine concentration and crystallization. This research investigated removal of dissolved silica from simulated HERO concentrate solutions using electrocoagulation (EC) with mild steel anodes and chemical coagulation with FeCl 3. At pH values of above 10, the mild steel anodes immediately passivated and were not able to deliver Fe 2+ ions into the solution. This necessitated lowering the solution pH value via HCl or FeCl 3 addition prior to EC. At pH values ≤10, iron dosing by EC was in agreement with that given by Faraday's law. The optimal initial pH value for operating the EC process was 8, which required addition of 17.8 mM HCl or 5.8 mM FeCl 3. An EC iron dose of 4.0 mM resulted in 76-89% silica removal for solutions with initial pH values between 4 and 8. Higher dosing up to 9.3 mM increased silica removal by only 5%. Chemical coagulation was not as effective as EC, and was able to achieve a maximum removal of 64% with a 4.0 mM FeCl 3 dose. Solution ionic strength had no measurable impact on silica removal by EC, but did affect final solution pH values and silica removal by chemical coagulation. For both EC and chemical coagulation, the initial pH value of solution had greater impact on silica removal than the iron dose.

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Silica removal to prevent silica scaling in reverse osmosis membranes

Cited by 52 publications

References 19 publications

Silica Fouling in Reverse Osmosis Systems–Operando Small-Angle Neutron Scattering Studies

Silica Fouling in Reverse Osmosis Systems–Operando Small-Angle Neutron Scattering Studies

Preventing Silica Scale Formation Using Hydroxide Ions Generated by Water Electrolysis

Evaluating electrocoagulation and chemical coagulation for removing dissolved silica from high efficiency reverse osmosis (HERO) concentrate solutions

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