Removal Of Silica Research Articles

Applicability of iron based coagulants for pre-treatment of coal seam water

This study reports the novel application of iron based coagulants to remove dissolved species from coal seam water. Pre-treatment of coal seam (CS) water from coal seam gas operations is required to minimise fouling of downstream membranes. The behaviour of ferric chloride and ferric sulphate with both simulated and actual coal seam water was studied by jar tests. Dissolved silica was the major species eliminated by either coagulant with >80% removal for simulated coal seam water. Barium ions were highly removed, in contrast to magnesium. Salinity of the CS water sample influenced the coagulant ability to reduce dissolved silica which may be due to differences in floc structure and the cation demand of the solution. Varying the simulated CS water composition revealed that silica removal could be promoted albeit it was not clear this outcome was related to the presence of a particular species in solution. Use of real CS water resulted in inhibition of the silica removal mechanism which was ascribed to the presence of organic materials and turbidity which were not accounted for in simulated solutions. Residual iron levels also seemed to increase when real CS water was tested, and with ferric sulphate the issue of contamination of treated water with sulphate species arose, an issue which may impact downstream membrane fouling. As dissolved silicates and alkaline earth ions are of primary concern relating to scaling of water treatment equipment and membranes, a deeper understanding of coagulant performance is warranted.

Pre-process desilication of wheat straw with citrate

Abstract Effects of treatment time, citrate concentration, temperature, and pH on Si extraction from wheat straw prior to hydrothermal pretreatment were investigated for maximising Si removal and biomass recovery before biomass refining. With citrate, an almost linear negative correlation between Si content in the residual biomass and treatment temperature was observed up to 170 °C, yielding a Si removal of up to 97.7%. This high Si removal came at the expense of a low mass yield (down to 45%) in the insoluble lignocellulosic fraction. Optimum process conditions for high Si removal and high total mass yield were: 100 mM sodium citrate, 130 °C, 60 min, 2% w/v solids, and pH of ∼6.5 during extraction. Using the proposed process conditions, silica removal of up to 77% was achieved with a mass yield of 72.8%. This Si removal from the insoluble lignocellulosic fraction did not affect the enzymatic cellulose hydrolysis, neither negatively nor positively.

Effectiveness of aluminium based coagulants for pre-treatment of coal seam water

Brackish coal seam water produced from the coal seam gas (CSG) industry is often treated by reverse osmosis to make the water suitable for beneficial reuse. As such, pre-treatment technologies are required in order to minimise membrane fouling. It was our hypothesis that coagulants may be able to remove problematic dissolved ions such as alkaline earth ions and soluble silicate species which are responsible for scaling of membranes and equipment. Consequently, this study evaluated the performance of aluminium chlorohydrate and aluminium sulphate coagulants for both simulated coal seam water and water collected from operating CSG wells. For simulated coal seam water samples the degree of dissolved silica removal was generally high (>85%) and promoted by increasing water salinity. Aluminium sulphate was better at removing silica (c.f. 94–92%), barium (c.f. 87–20%), strontium (c.f. 66–15%) and magnesium (c.f. 16–7.5%) and worse at removing calcium (44–65%) compared to aluminium chlorohydrate from simulated coal seam water, respectively. Variation in coal seam water composition of relatively concentrated solutions detrimentally impacted alkaline earth ion removal and in some instances reduced the extent of dissolved silica removal. When coal seam water samples for operating wells were studied, the amount of aluminium chlorohydrate required was significantly increased and the silica removal process inhibited (50% compared to 92% for simulated CS water). It was proposed that the presence of organic species in the real coal seam water played an important role in the mode by which the coagulants operated. Future studies should focus on understanding in more detail the influence of organic matter and influence of dissolved cations and anions upon coagulant behaviour.

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

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 FeCl3. At pH values of above 10, the mild steel anodes immediately passivated and were not able to deliver Fe2+ ions into the solution. This necessitated lowering the solution pH value via HCl or FeCl3 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 17.8mM HCl or 5.8mM FeCl3. An EC iron dose of 4.0mM resulted in 76–89% silica removal for solutions with initial pH values between 4 and 8. Higher dosing up to 9.3mM 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 4.0mM FeCl3 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.

Low-temperature precausticizing — a hopeful approach for green liquor desilication

We investigated silica removal by low-temperature precausticizing and the properties of second causticizing calcium carbonate (CCC). The results showed that about 89.3% of silica removal was achieved when 20% (the stoichiometric ratio) of causticizing quicklime was added for precausticizing at 20ºC for 60 min. After that, silica removal became slow. When no precausticizing quicklime was used to remove silica, the CCC particles had a rhombohedral crystal structure covered with amorphous material. As precausticizing quicklime was increased to 30%, the amorphous material and the crack disappeared, and the specific surface area decreased significantly. When CCC was used as filler, the Cobb value decreased significantly, and the sizing effect improved as precausticizing quicklime increased.

Laboratory-scale study of the advanced Fenton process for silica removal from brackish underground water in arid areas in Saudi Arabia

Laboratory-scale study of the advanced Fenton process for silica removal from brackish underground water in arid areas in Saudi Arabia

Surface sodium functionalization of ordered mesoporous Co3O4 controls the enhanced simultaneous catalytic removal of soot and NOx

We demonstrate a simple surface sodium functionalization effect introduced during silica removal step for controlling the enhanced simultaneous catalytic removal of soot and NOx by ordered mesoporous Co3O4.

Hybrid electrolysis–crystallization system for silica removal from aqueous solutions

The silica scaling difficulty is widely encountered in many industrial operations, including cooling towers, saline waters desalination systems and processes for produced water reuse. The common method of silica removal is to precipitate it at alkaline pH using metal hydroxides. A convenient way for achieving a high pH is by applying an electric current in an electrochemical cell. Silica removal was investigated using a novel hybrid electrochemical–crystallization technique at which the cathode serves only as the means for generating hydroxyl ions, and the precipitation reaction is performed in a separate crystallizer seeded with suspended particles. In this configuration, the anode and the cathode are separated by a cation exchange membrane. A high silica removal of 92% was readily achieved, by an adsorptive process involving magnesium hydroxide, at the optimal magnesium to SiO2 molar ratio of 4:1, pH of 10.8 and current density of 200A/m2.

Pilot-scale study of the radiation-induced silica removal from underground brackish water in Saudi Arabia

Abstract Silica scaling deposition in industrial water systems is one of the biggest challenges facing the water treatment industry due the low solubility of the scalants in the feed waters. In this preliminary work, we investigated the effectiveness of the ionizing radiation induced removal of silica in water sample from the Salbukh, Saudi Arabia, water treatment plant by using metallic iron as the source of ferric hydroxide to co-precipitate the silica. The influence of several reaction parameters, i.e. iron powder dosage, radiation dose, initial pH and equilibrium pH effect were investigated. In the optimum conditions, up to 75% of silica was removed. This preliminary study showed that this environmentally friendly process is effective in silica removal from underground water.

Beneficiation of Aluminum-, Iron-, and Titanium-Bearing Constituents from Diasporic Bauxite Ores

In this study, extraction of aluminum-, iron-, and titanium-bearing constituents from diaspore-type bauxite ores was investigated by stepwise treatment consisting of pre-desilication via alkali-leaching of bauxite ore, extraction of alumina via Bayer process, and recovery of iron from red mud via magnetic separation. The pre-desilication results showed that the removal of silica reached 73.92% and that the mass ratio of alumina to silica (A/S) of bauxite concentrate increased from 2.92 to 9.25 under the conditions of sodium hydroxide concentration of 50 wt.%, leaching temperature of 95°C, leaching time of 30 min, and liquid-to-solid ratio of 5 mL/g. A total of 96.31% alumina was extracted from the bauxite concentrate via the Bayer process. Subsequently, by using two-step magnetic separation (intensity: 0.8 T and 0.2 T), TiO2-bearing iron concentrate with total iron grade of 56.39% and TiO2 grade of 8.66% was obtained with recoveries of iron and TiO2 of 55.79% and 17.37%, respectively. The grade of TiO2 reached 21.22% in the nonmagnetic fraction.

Recovery of some valuable components from industrial waste

ABSTRACTThe present work studied several ways for wastewater treatment for the waste from the pulp and paper industries including the recovery of some valuable components from this waste and reaching the acceptable environmental limits for the treatment of waste. The acidification technique showed high efficiency for the removal of solids from the black liquor. A proper treatment for the effluent produced from the pulp and paper industry that used rice straw as raw material. The dose of the alum as a coagulant has an effect on the solid process and is due to the high percentage of solids in the black liquor. Hydrochloric acid is used to control the pH of the solution and separating most of the solids from the black liquor. Sodium hydroxide can be used to remove silica from the other solids by forming sodium silicate. The amount of solids precipitated increased by increasing the stirring time, temperature, rpm of the agitator, and decreasing pH. IR spectroscopy was carried out on the solid to assign the functional groups. Thermal analysis and EDX analysis were done to study the thermal properties of the solids. A proper design of the mixer and drier is accomplished to provide high efficiency of the silica removal process.

General Synthesis of N-Doped Macroporous Graphene-Encapsulated Mesoporous Metal Oxides and Their Application as New Anode Materials for Sodium-Ion Hybrid Supercapacitors

A general method to synthesize mesoporous metal oxide@N-doped macroporous graphene composite by heat-treatment of electrostatically co-assembled amine-functionalized mesoporous silica/metal oxide composite and graphene oxide, and subsequent silica removal to produce mesoporous metal oxide and N-doped macroporous graphene simultaneously is reported. Four mesoporous metal oxides (WO3− x , Co3O4, Mn2O3, and Fe3O4) are encapsulated in N-doped macroporous graphene. Used as an anode material for sodium-ion hybrid supercapacitors (Na-HSCs), mesoporous reduced tungsten oxide@N-doped macroporous graphene (m-WO3− x @NM-rGO) gives outstanding rate capability and stable cycle life. Ex situ analyses suggest that the electrochemical reaction mechanism of m-WO3− x @NM-rGO is based on Na+ intercalation/de-intercalation. To the best of knowledge, this is the first report on Na+ intercalation/de-intercalation properties of WO3− x and its application to Na-HSCs.

Modified Rice Straw as a Template in Syntheses of Nano TiO2 Loaded on Wool Fibers for Wastewater Treatment

ABSTRACTIndustrialization of textile produces large amounts of colored wastewater and recycling of that wastewater is recently under the scope. The current work is implemented to use rice straw as a template for preparation of nano TiO2 to be applied in decolorization of wastewater of textile industries. Different treatments including silica removal and esterification were performed for rice straw to produce highly reactive nanotitanium dioxide. Size, morphological shape, and surface area of the so obtained TiO2 nanoparticles were observed to be influenced by rice straw treatments. Percentage of anatase phase in titanium dioxide was increased from 41.6% to 75.0% after removing of silica and modification with citric acid of rice straw. The particle size of anatase was significantly reduced from 88.6 nm to 10.5 nm while the BET surface area of nanotitanium dioxide was enlarged from 41.2 m2/g to 84.7 m2/g. The prepared TiO2 nanoparticles were loaded onto wool fibers and the photocatalytic properties of nano TiO2 powder before and after loaded to fiber were measured against methylene blue dye. The dye removal percentage raised from 92.5 to 99.2 by using of nano TiO2 powder-loaded wool fibers compared to nano TiO2 powder.

Novel nanoporous N-doped carbon-supported ultrasmall Pd nanoparticles: Efficient catalysts for hydrogen storage and release

The reversible reactions involving formate and bicarbonate can be used to store and release hydrogen (H2), allowing H2 to serve as an effective energy carrier in energy systems such as fuel cells. However, to feasibly utilize these reactions for renewable energy applications, efficient catalysts that can reversibly promote both reactions are required. Herein we report the synthesis of novel polyaniline (PANI)-derived mesoporous carbon-supported Pd nanoparticles, or materials that can efficiently catalyze these reversible reactions. The synthesis involves pyrolysis of PANI/colloidal silica composite materials at temperatures above 500°C, followed by removal of the colloidal silica from the carbonized products with an alkaline solution and finally deposition of Pd nanoparticles within the mesoporous carbon products. The resulting nanomaterials efficiently catalyze the reversible reactions, i.e., the dehydrogenation of formate (HCO2‾+H2O→H2+HCO3‾) and the hydrogenation of bicarbonate (H2+HCO3‾→H2O+HCO2‾). The porosity and the catalytic property of the materials can be tailored, or improved, by changing the synthetic conditions (in particular, the pyrolysis temperature and the amount of colloidal silica used for making the materials). The study further reveals that having an optimum density of N dopant species in the catalysts makes Pd to exhibit high catalytic activity toward both reactions. Among the different materials studied here, the one synthesized at 800°C with relatively high amount of colloidal silica template gives the best catalytic activity, with a turnover frequency (TOF) of 2,562h−1 for the dehydrogenation reaction and a turnover number (TON) of 1,625 for the hydrogenation reaction.

Tailoring porosity in carbon spheres for fast carbon dioxide adsorption

Highly-porous carbon spheres were prepared by modified Stöber method combined with silica templating and CO2 activation. Silica was delivered in the form of either colloids or tetraethyl orthosilicate and used to create porosity. Subsequently, CO2 activation was used to develop microporosity. CO2 activation was done either: (1) on carbon spheres, following silica etching or (2) on silica-carbon composites, before silica removal. Both methods delivered carbon materials with well-developed structures and, importantly, preserved spherical morphology. Still, activation of the silica-carbon composites with subsequent silica etching afforded carbons with better structural properties and CO2 adsorption. Between materials prepared with silica colloids and TEOS-generated silica, the former showed more developed structures. The best material had specific surface area reaching 1500 m2 g−1 and total pore volume exceeding 1.2 cm3 g−1 and showed CO2 uptakes as high as 7.8 mmol g−1 (0 °C, 1 bar) and 4.0 mmol g−1 (23 °C, 1 bar). Mesoporosity improved mass transfer, which directly translated to faster CO2 equilibration (30–40% on average). The proposed synthesis afforded carbons with high and fast CO2 adsorption, which makes them good candidates for CO2 sorption applications. Moreover, it was shown that both, microporosity and mesoporosity, are important in development of prospective CO2 sorbents.

Dry Sintering Meets Wet Silver‐Ion “Soldering”: Charge‐Transfer Plasmon Engineering of Solution‐Assembled Gold Nanodimers From Visible to Near‐Infrared I and II Regions

AbstractAchieving highly tunable and localized surface plasmon resonance up to near infrared (NIR) regions is a key target in nanoplasmonics. In particular, a self‐assembly process capable of producing highly uniform and solution‐processable nanomaterials with tailor‐made plasmonic properties is lacking. We herein address this problem through a conjunctive use of wet Ag+ soldering and dry thermal sintering to produce nanodimer‐derived structures with precisely engineered charge‐transfer plasmon (CTP). The sintered dimers are water soluble, featuring gradually shifted CTP spanning an 800 nm wavelength range (up to NIR II). Upon silica removal, the products are grafted by DNA to offer surface functionality. This process is also adaptable to DNA‐linked AuNP dimers toward plasmonic meta‐materials via DNA‐guided soldering and sintering.

Dry Sintering Meets Wet Silver-Ion "Soldering": Charge-Transfer Plasmon Engineering of Solution-Assembled Gold Nanodimers From Visible to Near-Infrared I and II Regions.

Achieving highly tunable and localized surface plasmon resonance up to near infrared (NIR) regions is a key target in nanoplasmonics. In particular, a self-assembly process capable of producing highly uniform and solution-processable nanomaterials with tailor-made plasmonic properties is lacking. We herein address this problem through a conjunctive use of wet Ag+ soldering and dry thermal sintering to produce nanodimer-derived structures with precisely engineered charge-transfer plasmon (CTP). The sintered dimers are water soluble, featuring gradually shifted CTP spanning an 800 nm wavelength range (up to NIR II). Upon silica removal, the products are grafted by DNA to offer surface functionality. This process is also adaptable to DNA-linked AuNP dimers toward plasmonic meta-materials via DNA-guided soldering and sintering.

Preparation and characterization of single-handed helical carbonaceous nanofibers using 1,4-phenylene bridged polybissilsesquioxanes

Single-handed helical carbonaceous materials attracted much attention for varieties of potential applications. Herein, single-handed helical 1, 4-phenylene bridged polybissilsesquioxane nanofibers were prepared through a supramolecular templating approach using a pair of enantiomers. After carbonization at 700 °C for 2.0 h and removal of silica using HF aqueous solution, single-handed helical carbonaceous nanofibers were obtained. The obtained samples were characterized using the field-emission scanning electron microscopy, transmission electron microscopy, N2 sorptions, X-ray diffraction, Raman spectroscopy and diffuse reflectance circular dichroism (DRCD). The Raman spectrum indicated that the carbon was amorphous. The DRCD spectra indicated that the carbonaceous nanofibers exhibited optical activity. The surface area of the left-handed helical carbonaceous nanofibers was 907 m2/g. Such material has potential applications as chirality sensor and supercapacitor electrode.

Preparation of porous bio-char and activated carbon from rice husk by leaching ash and chemical activation.

Preparation porous bio-char and activated carbon from rice husk char study has been conducted in this study. Rice husk char contains high amount silica that retards the porousness of bio-char. Porousness of rice husk char could be enhanced by removing the silica from char and applying heat at high temperature. Furthermore, the char is activated by using chemical activation under high temperature. In this study no inert media is used. The study is conducted at low oxygen environment by applying biomass for consuming oxygen inside reactor and double crucible method (one crucible inside another) is applied to prevent intrusion of oxygen into the char. The study results shows that porous carbon is prepared successfully without using any inert media. The adsorption capacity of material increased due to removal of silica and due to the activation with zinc chloride compared to using raw rice husk char. The surface area of porous carbon and activated carbon are found to be 28, 331 and 645 m2 g−1 for raw rice husk char, silica removed rice husk char and zinc chloride activated rice husk char, respectively. It is concluded from this study that porous bio-char and activated carbon could be prepared in normal environmental conditions instead of inert media. This study shows a method and possibility of activated carbon from agro-waste, and it could be scaled up for commercial production.

Aqueous silica removal from agricultural drainage water and reverse osmosis concentrate by brackish water diatoms in semi-batch photobioreactors

Abstract A novel aqueous silica removal process using naturally occurring diatoms for water and wastewater treatment, in particular water reuse and desalination, was developed. Brackish agricultural drainage water containing 39 mg L−1 of total silica and 10 g L−1 of total dissolved solids was used as a source of silica-assimilating diatoms. The drainage water was statically incubated in 500-mL and 7.5-L photobioreactors at 27 ± 2 °C under continuous illumination using two 13-W compact fluorescent light bulbs as a light source. After 10 days, brown algal biomass became noticeable and silica removal started to occur. Silica removal accelerated as algal biomass accumulated. In the fourth semi-batch cycle, more than 95 % of molybdate reactive silica was removed within 28 h. Removal of nonreactive silica was also confirmed. Reverse osmosis concentrate samples from advanced water reclamation facilities with high silica concentration (>120 mg L−1) were also tested. More than 75 % of silica was removed within 6 days. Microscopic analysis revealed the presence of Pseudostaurosira, Nitzschia, and Halamphora species in the photobioreactors. To the best of our knowledge, this is the first report on the use of diatoms for aqueous silica removal in water treatment.