Removal Of Silica Research Articles

Electrochemical grafting of organic films on silica.

Traditionally, self-assembled monolayers formed on silicon require the removal of the insulating and chemically inert silica layer that naturally forms on the surface of crystalline silicon. The removal of silica is thought to be necessary in order to expose the conducting Si-H surface, which is reactive towards molecules. Here we report the unexpected result of electrochemical formation of thin organic films on silica-terminated silicon with silica thickness up to 20 nm. The process is facilitated by the electrochemical generation of aryl radicals that react with silanol groups at the distal end of silica.

Hazardous Fluoride and Silica Removal from Semiconductor Wastewater in a Waste Control by Waste Principle

Hazardous Fluoride and Silica Removal from Semiconductor Wastewater in a Waste Control by Waste Principle

Calcium and silica removal from water in evaporative cooling systems, using precipitation and electrocoagulation

Calcium and silica removal from water in evaporative cooling systems, using precipitation and electrocoagulation

Reusable Co-nanoparticles for general and selective N-alkylation of amines and ammonia with alcohols.

A general cobalt-catalyzed N-alkylation of amines with alcohols by borrowing hydrogen methodology to prepare different kinds of amines is reported. The optimal catalyst for this transformation is prepared by pyrolysis of a specific templated material, which is generated in situ by mixing cobalt salts, nitrogen ligands and colloidal silica, and subsequent removal of silica. Applying this novel Co-nanoparticle-based material, >100 primary, secondary, and tertiary amines including N-methylamines and selected drug molecules were conveniently prepared starting from inexpensive and easily accessible alcohols and amines or ammonia.

Photonic Crystal Film Preparation and Characterization for Chemical Sensing

Functionalized photonic crystal films were prepared for sensing small chemical molecules. First, silica nanospheres were self-assembled to form a colloidal crystal template within a mold. The interstitial space of this template was infiltrated by the hydrogel precursors, which were then allowed to polymerize. Upon removal of silica by hydrofluoric acid etching, a photonic crystal film, which produced a pink structural color, was formed. To add a chemical sensing functionality to the film, the molecules to be sensed were mixed with the hydrogel precursors for molecular imprinting; the amino acid proline was used for this purpose. Characterization of the functionalized photonic crystal film was conducted by optical reflectance measurements and imaging. The nanopores were imaged using SEM after cryogenic freezing of the film samples. Chemical sensing of proline was conducted on the film, with the reflectance peak shifting from 650 nm to

Geochemistry of tourmaline of elbaite-dravite series from sapphire bearing pegmatites, proterozoic higher Himalayan Crystalline Complex Jammu and Kashmir, India: Implication for evolution of pegmatite melt

Tourmaline of rare elbaite-dravite series has been reported for the first time from the sapphire bearing pegmatite from the Paddar area, Kishtwar District (Jammu and Kashmir), India. The sapphire-bearing pegmatites are hosted by ultramafic rocks of the Higher Himalayan Crystalline metamorphic complex. These pegmatites are dominantly composed of sodic-plagioclase, perthite, tourmaline, and sapphire, whereas microcline, biotite, and muscovite make up the minor phases. The tourmaline from these pegmatites contains high Mg, Ca, Na, and F content as well as low K, Fe, and Cr content. They are classified as alkali tourmaline, characterized by higher Mg/Mg + Fe and Na/Na + Ca ratios. They display complex substitution mechanisms during the crystallization (Li + Al↔Mg, Fe↔Mg, Na↔Ca, B + Al↔Si) and post crystallization alteration by the hydrothermal fluids. The geochemistry of tourmaline suggests that the tourmaline is crystallized from peraluminous, silicious pegmatitic melt (enriched in Al, Li, B, and H2O). This melt was most likely formed through partial melting of the metasediments of Higher Himalaya Crystalline during the M2 phase of regional metamorphism. The pegmatitic melt was injected in the ultramafics, resulting in bimtasomatism reaction evidenced by the development of systematic alteration zones next to the contact. Bimetasomatism results in the diffusion of the Ca and Mg from host rock to pegmatitic melt, and removal of silica from the pegmatitic melt, which leads to the increase of Al in pegmatitic melt. Finally, a saturation of the Al in the melt with a high Mg influx from host rock results in the favourable environment for crystallization of Mg-rich tourmaline and sapphire.

Joule-Heated Layered Double Hydroxide Sponge for Rapid Removal of Silica from Water.

Dissolved silica is a major concern for a variety of industrial processes owing to its tendency to form complex scales that severely deteriorate system performance. In this work, we present a pretreatment technology using a Joule-heated sponge to rapidly remove silica from saline waters through adsorption, thereby effectively mitigating silica scaling in subsequent membrane desalination processes. The adsorbent sponge is fabricated by functionalizing two-dimensional layered double hydroxide (LDH) nanosheets on a porous, conductive stainless-steel sponge. With the application of an external voltage of 4 V, the Joule-heated sponge achieves 85% silica removal and 95% sponge regeneration within 15 min, which is much more efficient than its counterpart without Joule-heating (360 min for silica adsorption and 90 min for sponge regeneration). Material characterization and reaction kinetics analysis reveal that electrostatic interactions and "memory effect"-induced intercalation are the primary mechanisms for silica removal by the LDH nanosheets. Moreover, Joule-heating reduces the boundary layer resistance on nanosheets and facilitates intraparticle diffusion of dissolved silica, thereby increasing silica removal kinetics. Joule-heating also enhances the release of silicate ions during the regeneration stage through exchange with the surrounding anions (OH- or CO32-), resulting in a more efficient sponge regeneration. Pretreatment of silica-rich feedwaters by the Joule-heated sponge effectively reduces reverse osmosis membrane scaling by amorphous silica scale, demonstrating great potential for silica scaling control in a broad range of engineered processes.

Kinetic Laws of the Removal of Silica from an Alkaline Solution of Sodium Aluminate

Kinetic Laws of the Removal of Silica from an Alkaline Solution of Sodium Aluminate

Pengaruh Pemberian Sumber Silikon pada Sifat Kimia dan Pertumbuhan Tanaman Padi pada Tiga Jenis Tanah

Silicon (Si) has an important role in the growth of rice plants and some soil chemical properties. However, Si still receives less attention, because there is still little information about the importance of Si for rice plants and not many researches have been done on the use of Si in rice plants. This condition causes the farmers do not practice the use of Si as a fertilizer that eventually removal or release of silica from the soil solum. One source of Si that can be used as a fertilizer is trass. Currently, the trass has been widely used by the community as the basic material for making bricks. However, the use of trass as a source of Si in agriculture is not widely known. Therefore, it is necessary to evaluate the effect of trass on rice plant growth and soil chemical properties. The purpose of this study was to analyze the effect of trass addition on soil chemical properties and rice growth. The experimental design used was a separate plot where three types of soil, namely oxisol, inceptisol, and vertisol as the main plot and seven doses of trass were 0 (D0); 1.25 (D1); 2.5 (D2); 3.75 (D3); 5 (D4); 7.5 (D5); and 10 (D6) g kg-1 of soil as sub-plots. The treatment was a combination of these two factors and was repeated 3 times to obtain 63 experimental units. The results showed that the administration of trass significantly increased pH, available P, Ca-dd, Mg-dd, and significantly decreased available Fe and Mn. Meanwhile, the provision of trass also significantly affected plant height, namely 91 cm, and the number of tillers, namely 21 stems. Key words: chemical properties, rice, silicon, trass

Plasma-assisted template removal and consolidation of silica coatings on polycarbonate

This paper presents a fast and efficient method of removing the template from silica thin films on polycarbonate. Radiofrequency-generated oxygen plasma induced the decomposition of the non-ionic surfactant. The reference samples were silica coatings on silicon, which had different pore sizes. We removed the surfactant by solvent extraction and calcination from these samples. Grazing incidence angle X-ray diffraction analysis shows a highly ordered arrangement of mesopores. The formation of the face-centred cubic structure of mesopores is independent of the substrate and the template removal method. Atomic force microscopy analysis showed open-pore channels after oxygen plasma etching. It also proved that the ammonia treatment increases the hardness of the layer. A short air-plasma treatment is effective for the consolidation of the silica layer and improves the abrasion resistance of the layer on polycarbonate. Air plasma treatment is an alternative to the long heat treatment process. We performed environmental tests according to the relevant ISO standards for optical coatings. Air plasma treated silica coatings have passed all the weathering tests. Therefore, it can be used in outdoor applications, such as a protective layer for the plastic cover of LED street lights. These thin films on polycarbonate have at least one year of service life and are weather-resistant. Plasma treatment can consolidate the silica network and the thin films on polycarbonate have high light transmission (T = 98.8 %).

Continuous Treatment of Oil-Sands Produced Water By Electrocoagulation

The treatment performance of electrocoagulation (EC) was investigated using continuous flow reactor for simultaneous removal of silica and hardness causing ions calcium and magnesium from produced water. The amount of charge passed per unit volume of produced water treated (i.e., the charge loading, C L- 1) was adjusted either by varying the electrode area or the current density, under a range of inlet flowrates (20―120 mL min-1) using Fe and Al electrodes. It was found that direct current (DC) EC operation with Fe electrodes was able to remove about 87% of the total silica, whereas with Al electrodes more than 95% silica removal was achieved. These removals were achieved with an influent silica concentration of 60 mg L- 1, a charge loading 2000 C L- 1, current density 8 mA cm- 2, pH of 7.75 and feed flow rate 60 mL min-1 (corresponding to a Reynolds number of 116). In addition, the calcium removal was observed to be around 85% with both Fe and Al electrodes. Al electrodes were found to be more effective for removal of magnesium achieving about 70% removal in comparison to 39% removal achieved with Fe electrodes at the same operating conditions.The average faradaic efficiency of DC-EC with Fe and Al electrodes was observed to be 99.9% and 149% respectively over the range of charge loading between (600―2000 C L- 1) and flow rate. The super faradaic efficiency of Al was due to the chemical dissolution of Al cathode which provides additional Al coagulant [1]. The specific energy consumption in DC-EC operation was found to be 1.79 and 1.76 kWh m- 3 for Fe and Al respectively at 2000 C L- 1, at a current density of 8 mA cm- 2 and a fixed Reynolds number of 116. During DC-EC operation, the cell voltage was found to increase in time, however this increase was reduced with the application of polarity reversal (PR-EC) [2]. It was found that a longer appropriate polarity reversal duration of 10 min provided sufficient time to remove the fouling / passivation layers from the electrode surface [1], [3]. Ca and Mg precipitates form a passivating layer in the alkaline pH on the cathode surface. This layer can be dissolved from the electrode surface by the acidic pH generated at the interface of the anode after polarity reversal [1]. This results in reduced cell voltage and hence energy consumption in comparison to DC-EC. PR-EC with 10 min reversal time reduced the energy consumption to 1.53 kWh m- 3 and 1.57 kWh m- 3 for Fe and Al electrodes respectively at the same operating conditions as for DC-EC discussed above. Under these conditions (charge loading = 2000 C L- 1, current density = 8 mA cm- 2), the silica removal was found to be only 65% with Fe electrodes, compared to above 95% with Al electrodes. Finally, the use of hybrid electrodes (Fe/Al) for DC-EC in which Fe was anode and Al as cathode produced a slightly higher cell voltage than non-hybrid Fe and Al, probably due to the more negative redox potential of the Al cathode. However, for PR-EC with a 10 min reversal time using a combination of electrodes (Fe/Al) had a similar cell voltage than for Fe or Al-EC. This hybrid electrode system had an energy consumption of about 1.53 kWh m- 3 while achieving 96% Si, 84% Ca and 73% Mg removal. The results indicate that EC can effectively remove silica and hardness causing ions from synthetic produced water while reducing the cell voltage with the application of PR. As shown in Fig. 1, a lower operating cost was estimated for Fe-EC due to the low cost of the metal consumption, since the cost of Al is around 2.8 times higher than the cost of Fe. The cost of metal consumption for the hybrid combination of Fe/Al electrodes was significantly lower than for Al-EC, while sustaining more than 95% Si removal.

Consecutive Organosolv and Alkaline Pretreatment: An Efficient Approach toward the Production of Cellulose from Rice Straw.

The efficient removal of silica from rice straw and separation of its major components is essential for further valorization to produce value-added products. With regard to this, the isolation of cellulose (CEL), hemicellulose (HEM), and lignin (LIG) is imperative but quite challenging. Among several pretreatments of lignocellulosic biomass, the organosolv approach is deemed as one of the promising methods. Here, we present two different two-step approaches for the removal of silica and disintegration of significant components from rice straw, especially CEL; (i) base pretreatment, followed by organosolv treatment in the presence of organic acid, and (ii) organosolv pretreatment in the presence of organic acid, followed by base treatment. After each treatment, the recovered solid components are confirmed by various characterization techniques such as Fourier-transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and thermogravimetric analysis. Method 2 demonstrates 82% total removal of HEM and LIG along with 90.4% of silica removal from rice straw to obtain CEL. Furthermore, the obtained crude CEL is found to be with a purity of 78%. Excellent removal of silica (90.4%) reflects that in a test study, the crude CEL obtained from method 2 gives a higher yield of butyl glucosides (59.6%) than rice straw, which affords 45.0% of butyl glucosides.

Break-even Analysis of Respirable Crystalline Silica (RCS) Exposure Interventions in the Construction Sector.

We investigated long-term economic impacts of respirable crystalline silica (RCS) removal interventions in the construction at the societal level. We estimated costs and benefits of two RCS exposure interventions, use of "respirators" and "wet method," over a 30-year time period. We identified economic impacts of the interventions under four different scenarios. Under current practices, we estimated that approximately 125 lung cancer cases attributable to RCS exposure would arise in 2060. Under the full exposure removal scenario, we estimated there would be 53 new cases. Over the 30-year time period, the estimated cumulative averted cases are 787 and 482 for respirators and wet method, respectively, which amount to net benefits of $422.13 and $394.92 million. Findings provide important information for policymakers seeking to reduce the economic burden of occupational lung cancer in society.

Simultaneous removal of silica and TOC from steam assisted gravity drainage (SAGD) produced water using iron-hydroxide-coated walnut shell filter media

Extracting Alberta’s bitumen by SAGD requires a growing supply of steam, which is mainly generated from recycled produced water (PW). Traditionally, a warm lime softener (WLS), followed by walnut shell filter (WSF) and weak acid cation exchange (WAC) units have been employed to minimize the concentrations of silica, TOC, and hardness from PW. In this study, we enhanced TOC and silica removal in a WSF unit by modifying the surface of the walnut shell media. The walnut shells were modified by anchoring low mass percentages (e.g., < 5 wt%) of iron(hydroxide) nanoparticles under moderate hydrolysis conditions. The nanoparticle-anchored walnut shell particles (WS-NPs) were fully characterized, and their ability to remove TOC and silica was tested using batch and column experiments. In the batch tests, up to 85 % of silica and TOC was removed. In the column tests, which mimicked industrial operations, WS-NPs significantly improved the breakthrough behavior without reaching pressure drop limitations. The column breakthrough behaviors were successfully described by a dimensionless advection-axial dispersion model. The model accurately captured the commercial breakthrough behavior, indicating the possibility of scaling up the filter using a combined unit that removes silica and TOC simultaneously without using WLS and WAC.

Silica Removal from a Paper Mill Effluent by Adsorption on Pseudoboehmite and γ-Al2O3

Effluent reuse is a common practice for sustainable industrial water use. Salt removal is usually carried out by a combination of membrane processes with a final reverse osmosis (RO). However, the presence of silica limits the RO efficiency due to its high scaling potential and the difficulty of cleaning the fouled membranes. Silica adsorption has many advantages compared to coagulation and precipitation at high pHs: pH adjustment is not necessary, the conductivity of treated waters is not increased, and there is no sludge generation. Therefore, this study investigates the feasibility of using pseudoboehmite and its calcination product (γ-Al2O3) for silica adsorption from a paper mill effluent. The effect of sorbent dosage, pH, and temperature, including both equilibrium and kinetics studies, were studied. γ-Al2O3 was clearly more efficient than pseudoboehmite, with optimal dosages around 2.5–5 g/L vs. 7.5–15 g/L. The optimum pH is around 8.5–10, which fits well with the initial pH of the effluent. The kinetics of silica adsorption is fast, especially at high dosages and temperatures: 80–90% of the removable silica is removed in 1 h. At these conditions, silica removal is around 75–85% (&lt;50 mg/L SiO2 in the treated water).

A low capital method for silicon interference in bamboo kraft pulping alkaline recovery system

The problem posed by the silicon interference in bamboo pulp black liquor has been troubling bamboo pulp mills as well as hindering the development of non-wood pulp mills. Silica is separated from bamboo pulp black liquor by acid precipitation, accompanied by the sediment of lignin, which is disadvantageous to alkali recovery system. The amount of carboxylate increases through the oxidation of lignin, and the solubility of lignin increases. So the lignin precipitation and the removal of silica can be quantified by the combination of acidification and light oxidation. For solving the problem, we separate the silicon in the black liquor through oxygen oxidation and carbon dioxide acidification without affecting the stability of the alkali recovery system. TG, combustion calorific value and visible light absorption are tested after oxidation and acidification. Finally, by comparing with the mature pulp black liquid alkali recovery system, it is concluded that when taking economic capital into consideration, oxidizing to pH 12.45(at 80 °C) and acidifying to pH 10 (at 50 °C) are suitable for our goal. In this case, the silicon removal rate reaches 76.41 wt%; the amount of separated lignin is 17.58 wt% and the calorific value loss of black liquor reaches 26.47%.

Effect of Liquid Hot Water Pretreatment on Hydrolysates Composition and Methane Yield of Rice Processing Residue

Lignocellulosic rice processing residue was pretreated in liquid hot water (LHW) at three different temperatures (140, 160, and 180 °C) and two pretreatment times (10 and 20 min) in order to assess its effects on hydrolysates composition, matrix structural changes and methane yield. The concentrations of acetic acid, 5-hydroxymethylfurfural and furfural increased with pretreatment severity (log Ro). The maximum methane yield (276 L kg−1 VS) was achieved under pretreatment conditions of 180 °C for 20 min, with a 63% increase compared to untreated biomass. Structural changes resulted in a slight removal of silica on the upper portion of rice husks, visible predominantly at maximum severity. However, the outer epidermis was kept well organized. The results indicate, at severities 2.48 ≤ log Ro ≤ 3.66, a significant potential for the use of LHW to improve methane production from rice processing residue.

Selective silica removal in geothermal fluids: Implications for applications for geothermal power plant operation and mineral extraction

Raw material extraction from geothermal fluids often comprises concentrating and cooling steps, which increases the risk of silica scaling formation. However, existing silica removal strategies do not consider the impact on raw material extraction. In this study, the applicability and element-selectivity of three silica removal techniques (seed-induced, lime and caustic precipitation) were tested in batch experiments using synthetic and natural geothermal fluid samples. Increasing the pH-value to 10.5 and the Ca/Si ratio > 1.25 was found to mitigate silica scaling effectively via formation of calcium-silicate-hydrate phases (C-S-H phases). The developed silica removal process does not affect the raw materials and is therefore suitable for brine mining purposes.

Pilot test of simultaneous removal of silica, hardness, and turbidity from gray water using circulating pellet fluidized bed

A pilot test was performed by applying a circulating pellet fluidized bed (CPFB) system during the simultaneous removal of silica, hardness, and turbidity from gray water generated from the coal gasification of a coal-to-liquids company in Shanxi Province, China. The effects of a magnesium agent (MgO) and coagulant (Al2(SO4)3) in the CPFB system on the simultaneous treatment of silica, hardness, and turbidity in gray water were investigated, and the removal mechanism was explored. The test results demonstrated that when the MgO and Al2(SO4)3 dosages were 500 mg/L and 660 mg/L, NaOH and polyacrylamide dosages were 200 mg/L and 4 mg/L, respectively, and the removal efficiencies of silica and total hardness exceeded 80% and 55% in the effluent, respectively, with the effluent turbidity remaining below 5 nephelometric turbidity units. The comprehensive cost of dosage agents was approximately 0.22 USD/m3. Physical characterizations of the sludge using scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy revealed that silica was primarily removed through silicate precipitation and adsorption by compounds such as Mg(OH)2. The findings confirmed that the CPFB technology can reduce the silica, total hardness, and turbidity contents within the desired range, and thus, this study provides useful design parameters and an engineering basis for the development of subsequent gray water treatment processes.

Experimental simulations of Zn[sbnd]Pb slag weathering and its impact on the environment: Effects of acid rain, soil solution, and microbial activity

Slag heaps are far from stable and evolve continuously from the time they are deposited. In the studied site (Świętochłowice, Upper Silesian Industrial Region, Poland), the major change in the slag heap has involved the formation of fine-grained strongly weathered material. Possible conditions of slag weathering, as well as any impacts of weathered material on the environment, have been evaluated by weathering experiments. The experiment simulating acid rain at adjusted pH = 4 precisely reproduced many features of the weathering transformations observed in nature, such as strong disintegration of slag material, formation of abundant Fe(hydro)oxides, silica and alumina removal, and Pb precipitation. Conversely, bioweathering with Acidithiobacillus thiooxidans often showed the opposite direction of transformations (Si and Al precipitation, Pb removal, transformations at the rims of larger slag particles), probably due to the too-aggressive low pH of the simulations. There are environmental consequences as more and more slag in the heap weathers, with fresh slag releasing mostly Zn and Ba. On the other hand, weathered slag material may release high contents of Pb, Cd, As, but only if the pH remains at 4–6. In present-day slag heap conditions, precipitation of Fe(hydro)oxides and other secondary phases diminishes toxic element mobility. However, soils and sediments surrounding the heap show high levels of contamination (up to 2500 mg/kg for Pb, up to 11,300 mg/kg for Zn, up to 120 mg/kg for Cd), which is perhaps due to leaching of weathered slag or its mechanical removal. Other contaminants include smelter emissions and high Ba and Hg components that are tentatively linked to the episode of early weathering of fresh slag.