Silica and metals removal by pretreatment to prevent fouling of reverse osmosis membranes

Reverse osmosis is being increasingly used for desalination of seawater, brackish water and as well the marginal and polluted wastewaters. The operation of waters bearing substantial amount of silica is only feasible if there is a chemical pretreatment in process to prevent excessive and unbearable fouling by this refractory deposit. In this study, model solutions representing tailings wastewater which usually has high silica content was used in standard jar tests using the Boltac Coagulation and Flocculation simulator to determine the effectiveness of chemical pretreatment (by precipitation and coagulation) for removal of silica and other species such as magnesium, calcium, iron and manganese which affect silica fouling. Two precipitants were tested: lime and soda ash, and caustic soda. Precipitant aids (alum and ferric chloride) were also examined in combination with optimum precipitant doses to observe their differential effects. The optimum precipitant dose of caustic soda was 200 mg/L. Ferric chloride and alum were tested with this optimum caustic soda dose, but did not improve removal significantly, if at all. The optimum precipitant dose of lime and soda ash was 150 mg/L lime and 450 mg/L soda ash. Ferric chloride and alum were tested with this optimum lime and soda dose, but again did not improve removal enough to warrant their use. Neither of the methods were as effective in removal of magnesium and calcium as in removal of other components; lime and soda ash treatment as expected actually increased the calcium content of solutions.     

Spectroscopic Investigation of the Coloration and Fabrication Conditions of Medieval Blue Glasses

Potash‐ and soda‐lime‐stained glasses from the 12th–13th centuries, blue‐colored by cobalt, have been investigated by Mn, Fe, and Cu K‐edge X‐ray and optical absorption spectroscopies in order to determine the oxidation state of these elements and their impact on the blue color. Remelting these historical glasses in air at 1200°C, the estimated temperature of medieval furnaces, revealed that these four glasses are more reduced before remelting. This favors Mn as weakly absorbing Mn²⁺, Fe as Fe²⁺ and Cu as colorless Cu⁺. Therefore Fe²⁺ is the second blue chromophore and copper was not intentionally used by glassmakers to obtain a blue color. A colorimetric analysis indicates that these specific melting conditions have a limited effect on the blue color of these glasses. Based on the spectroscopic determination of the redox state of Fe, Mn, and Cu, we estimate the oxygen partial pressure in medieval furnaces to be 10^?7–10^?9 and 10^?5 bar for the potash‐ and soda‐lime samples, respectively. The comparison with previous results enables to prove the evolution of furnace technology over centuries.     

A Novel Method for Preparing V-doped Titanium Dioxide Thin Film Photocatalysts with High Photocatalytic Activity Under Visible Light Irradiation

The liquid phase deposition (LPD) method was successfully used for preparing V-doped TiO₂ thin film photocatalysts. In this simple and easily-controlled process, V-doped anatase TiO₂ thin films were directly deposited on a soda lime glass substrate placed in an aqueous solution containing Ti- and V-fluoro complex ions, followed by annealing. The thin films were analyzed by XRD, XPS, UV-vis. V⁴⁺ ions were introduced into the lattice of TiO₂ through in-situ substituting Ti⁴⁺. The absorption edge of V-doped TiO₂ films shifted to visible light region. The highly efficient photocatalytic activity was verified by the decomposition of methylene blue under visible light irradiation.     

Steam reactivation of 16 bed and fly ashes from industrial-scale coal-fired fluidized bed combustors

The hydration behaviour of sixteen ashes, obtained from different commercial-scale fluidized bed combustors, has been investigated. Hydration is important for both ash disposal and reactivation of excess lime present in the ashes for further use in flue gas desulphurization. The techniques used were instrumental and conventional chemical analysis, thermogravimetry and X-ray diffraction. The ashes comprised both fly ash and bottom ash, with particle size less than 2 mm. The ashes were heat treated in air to oxidize free carbon and then hydrated with pressurized steam at about 170 °C, alone and with addition of pure CaO.It has been shown that steam hydration is effective in quantitatively converting CaO to Ca(OH)₂, but in most cases the free lime content (i.e. CaO+Ca(OH)₂), expressed as CaO, decreases and added CaO enters into pozzolanic reactions with coal ash components, in part or even completely. Both the chemical evidence and X-ray phase analyses indicate that hydrated silicates and silicoaluminates are formed. The hydrated ashes are all able to take up additional SO₂ and it appears that the presence of amounts of Ca(OH)₂ detectable by phase analysis is not necessary for such capture.     

Stabilization of PCC dispersions prepared directly in the mother-liquid after synthesis through the carbonation of (hydrated) lime

Various CaCO₃-based products are often used in the form of concentrated aqueous dispersions. This study investigates the stabilization of PCC dispersions prepared directly in the mother-liquid after the carbonation of (hydrated) lime through the adsorption of a commercial sodium polyacrylate dispersant. The results demonstrate that the composition of the mother-liquid, particularly the Ca²⁺ activity, profoundly influences virtually all processes pertinent to dispersion stabilization—from the initial charging of the CaCO₃ surface in base PCC dispersions, to the surface charge regulation and dispersion stabilization efficiency of the polyacrylate dispersing agent. Rising prominence of the counterion condensation effects in Ca²⁺ rich solutions limits the conditions conducive to the surface charge regulation through dispersant adsorption to an optimum pH range of about 8-11. Furthermore, dispersion stability analysis, based on the classical DLVO theory of colloid stability, and corroborated by experimental evidence in the form of particle size distribution analyses, also indicates that optimum stability conditions for such PCC dispersions are established with small dispersant doses (0.25-0.5% per dry weight) in the pH range of about 9-11.     

A modified Solvay process with low-temperature calcination of NaHCO3 using monoethanolamine: Solubility determination and thermodynamic modeling

An energy-saving, modified Solvay process for dense soda ash production was proposed to replace the high-temperature, calcination step of NaHCO₃. We found NaHCO₃ completely decomposed into anhydrous, Na₂CO₃ at 353 K in a mixed-solvent containing at least 65 wt% of monoethanolamine (MEA), which is an amine-absorbent prevalently used for CO₂ capture. A chemical model was built after the determination of solubilities and through data regression for the solid–liquid system: Na-Cl-NH₄-CO₃-HCO₃-MEA-H₂O. Reparameterization for paired-ion interactions were performed via the mixed-solvent electrolyte model. Thermodynamic analysis elucidated the shift in ion dominance from HCO₃⁻ to CO₃²⁺, thereby providing the phase transition mechanisms. An exploratory, fed-batch experiment was implemented to verify the accuracy of the model, for which the obtained solids were in the form of saleable, dense soda ash products; bulk densities up to 1.01 g/cm³ were achieved in the laboratory.     

硝酸尾气净化制亚硝酸钙

选用价格低廉的石灰乳作为吸收液对硝酸尾气的吸收净化进行了研究，并在小试装置上进行了石灰乳与纯碱溶液的吸收对比实验。结果表明，石灰乳对NOX的吸收效果优于纯碱溶液，并且能够生产出合格的亚硝酸钙产品。     

Local structure of network modifier to network former ions in soda‐lime alumino‐borosilicate glasses

The structure of soda‐lime alumino‐borosilicate glass was studied using molecular dynamics simulations of samples of varying compositions containing ~20 000 atoms each. Pair distribution functions (PDFs) of cations to oxygen were used for comparison to available experimental data to evaluate consistency between simulations and experiment. Additional PDFs and coordination of the network forming cations (Al/B/Si) to network modifiers (Ca/Na) were examined, which is difficult to measure experimentally. The results are consistent with available experimental data regarding cation‐oxygen bond lengths and network former to oxygen coordination numbers. Si and Al are predominantly 4‐coordinated, with a small concentration of overcoordinated species similar to experimental data. B varied as 3‐coordinated, BO₃, and 4‐coordinated, BO₄, as a function of the amount of Ca²⁺ and Na⁺ present, the ratio of Al₂O₃ to B₂O₃, and the fictive temperature of the sample, similar to experimental data. The simulations provide new information regarding the locations on the network modifiers to the +3 cations, Al and B. For instance, one Al ion can have multiple Na within 4 Å, but also the Na can be within 4 Å of several +3 cations. Such results would indicate a greater complexity of local structure that goes beyond the stoichiometric one +1 modifier ion near one +3 network former or one +2 modifier near two +3 formers in tetrahedral sites.     

Study of a Chilean petroleum coke fluidized bed combustion fly ash and its potential application in copper, lead and hexavalent chromium removal

This work deals with the characterization of a circulated fluidized bed combustion (CFCB) Chilean petroleum coke fly ash (FA) from a petroleum coke power plant, and its potential use in neutralization and heavy metals removal from acid wastewaters. FA presents a high Ca and content, being anhydrite the major crystalline mineral phase, with minor proportions of calcite, portlandite and lime. Regarding to environmental characterization of this fly ash, leaching tests allowed concluding that FA is a non-hazardous residue. Heavy metals removal tests indicate that FA is able to remove Cu²⁺ and Pb²⁺ mainly due to a precipitation process, while Cr(VI) is being removed probably due to a reduction process to Cr(III), at high liquid to solid ratios. Cu²⁺, Pb²⁺ and Cr(VI) kinetic experimental data present acceptable fit to a pseudo-second order kinetic model. According to these results, FA may be used to remove heavy metals and neutralize acid wastewaters, suggesting a possible replacement of pure and costly alkaline materials.     

Hydronium Ions in Soda‐lime Silicate Glass Surfaces

The presence of leachable alkali ions, or their hydrated sites in the glass, is believed to be a determining factor for the interfacial water structure at the glass surface, influencing the surface properties of glass. The interfacial water structure on soda‐lime silicate glass in humid ambience at room temperature was analyzed with sum‐frequency‐generation (SFG) vibration spectroscopy, which can probe the interfacial water layer without spectral interferences from the gas phase water. The soda‐lime glass surface exposed to water vapor shows three sharp SFG peaks at 3200, 3430, and 3670 cm^?1 in SFG, which is drastically different from the SFG spectra of the water layers on the fused quartz glass surface and the liquid water/air interface. The sharp peak at 3200 cm^?1 is believed to be associated with the hydronium ions in the Na⁺‐leached silicate glass surface. The 3200 cm^?1 peak intensity varies with the relative humidity, indicating its equilibrium with the gas phase water. It is proposed that the hydronium ions in the Na⁺‐leached sites produce compressive stress in the silicate glass surface; thus the growth of hydronium ions with increasing humidity might be responsible for the increased wear resistance of soda‐lime glass surfaces in near‐saturation humidity conditions.     

Observation of Crack Propagation in Glass Using X-ray Phase Contrast Imaging

High-speed X-ray phase contrast imaging synchronized with a Kolsky bar apparatus was utilized to investigate the cracking behavior of a borosilicate glass, a soda lime glass, and a glass ceramic in front of a cylindrical projectile with an impact velocity of 5 ms⁻¹. For each material, three different surface conditions were prepared for the impacted edge of the specimen. Angular cracking was observed in front of the projectile for borosilicate glass. For soda lime glass, straight cracking was observed. For glass ceramic, curved cracking was observed in front of the projectile. Cracking behavior was observed to be independent of the surface condition on the impacted edge.     

Reactions catalyzed by soda lime glass. II. Polymerization of methyl methacrylate

Rates of sodium bisulfite-initiated polymerization of methyl methacrylate (MMA) in water were determined in the presence and absence of colorless and colored soda lime glass (amber glass). The rate of polymerization increased in the presence of glass. For example, the rate of polymerization increased from 1.3 × 10^?5 mole/(1.sec) to 3.9 × 10^?5 mole/(1.sec) when amber glass (200 mesh) concentration was varied from 0 to 30 g/l. of the reaction mixture at 40°C. It was found that the finer the particle size of the soda lime glass, the higher was the conversion percentage of monomer to polymer. A glass–polymer combination containing 20 g glass was prepared and subjected to Soxhlet extraction with benzene; the insoluble polymer part was found to increases as initiator concentration was decreased.     

Properties of high-volume fly ash concrete incorporating nano-SiO2

This paper presents a laboratory study on the properties of high-volume fly ash high-strength concrete incorporating nano-SiO₂ (SHFAC). The results were compared with those of control Portland cement concrete (PCC) and of high-volume fly ash high-strength concrete (HFAC). Assessments of these concrete mixes were based on short- and long-term performance. These included compressive strength and pore size distribution. Significant strength increases of SHFAC compared to the high-volume fly ash high-strength were observed as early as after 3 days curing, and improvements in the pore size distribution of SHFAC were also observed. In this work, the hydration heat of nano-SiO₂ fly ash cement systems was also studied in comparison to the fly ash-cement systems and to the pure cement systems. In addition, the weight change of fly ash incorporating nano-SiO₂, fly ash, and nano-SiO₂ alone after immersed in saturated lime solution was also studied.     

An investigation on effects of various parameters on viscosities of coal–water mixture prepared with Erzurum–Aşkale lignite coal

In this study the effects of parameters such as coal loading (wt.%), the initial pH of mixture, the addition of various electrolytes, surfactants and temperature on the viscosity and rheologic parameters of coal–water mixture (CWM) have been investigated. The apparent viscosity was measured with a RV8-Brookfield rotating type viscosimeter. The additives used were AlCl₃ and K₂HPO₄ as the electrolytes and Cetyltrimethyl Ammonium Bromide (CTAB), Sodium Dodecyl Sulphate (SDS) and Borrosperse NA-3A as the surfactants. It was found that the most effective additives, in terms of the viscosity reduction, were CTAB and K₂HPO₄, and that the CWM which had coal concentrations up to 50% (based on the weight of dry coal) could be prepared by using each additives. In addition, the viscosities of CWM with increasing temperature were found to increase at low speed, and decrease at high speed.     

Microporous glass ceramics from combination of silicate,borate and phosphate wastes

Abstract

Borate mineral wastes and phosphate ash resulting from the incineration of meat and bone meal represent two particularly abundant inorganic wastes. This paper is dedicated to the combination of such wastes, together with kaolin clay, focused on the development of highly porous ceramic bodies. Borate waste has a multiple effect, providing liquid phase at the sintering temperature (1050°C), gas release (from the decomposition of its calcite fraction) and a CaO source, which reacts with residues from clay and promotes the formation of anorthite crystals as a newly formed phase. Control of the heating rate, i.e. adoption of fast heating (20°C min^?1) and, above all, introduction of recycled soda–lime–silica glass as secondary additive, allowed obtaining lightweight microporous bodies (density below 0·45 g cm^?3) with uniform pore structure that could be useful for thermal and acoustic insulations.     

Utilization of fly ash coming from a CFBC boiler co-firing coal and petroleum coke in Portland cement

Fly ash coming from a circulating fluidized bed combustion (CFBC) boiler co-firing coal and petroleum coke (CFBC fly ash) is very different from coal ash from traditional pulverized fuel firing due to many differences in their combustion processes, and thus they have different effects on the properties of Portland cement. The influences of CFBC fly ash on the strength, setting time, volume stability, water requirement for normal consistency, and hydration products of Portland cement were investigated. The results showed that CFBC fly ash had a little effect on the strength of the Portland cement when its content was below 20%, but the strength decreased significantly if the ash content was over 20%. The water requirement for normal consistency of cement increased from 1.8% to 3.2% (absolute increment value) with an addition of 10% CFBC fly ash; and the free lime (f-CaO) content of CFBC fly ash affected the value of increasing. The setting time decreased with an increase of CFBC fly ash content. The volume stability of the cement was qualified even when the content of SO₃ and f-CaO reached 4.48% and 3.0% in cement, respectively. The main hydration productions of cement with CFBC fly ash were C-S-H (hydrated calcium silicate), AFt (ettringite), and portlandite.     

Fully sintered alumina with a higher Vickers hardness prepared using a gel-casting process

The dispersant (commercial ammonium polyacrylate), sintering additive (Mg²⁺), and chelating agent (EDTA) effects on the Zeta potential and rheological behavior of alumina slurry with high solid content were investigated. The alumina ceramic green microstructures and sintered microstructures prepared using slurries with different additives using the gel-casting process were also studied. It was observed that the dispersion deteriorated after adding Mg²⁺. Slurry simultaneously added with dispersant and EDTA-chelated Mg²⁺ produced higher absolute Zeta potential value and low viscosity due to EDTA chelating with Mg²⁺. The sample added with dispersant and EDTA-chelated Mg²⁺ exhibited a uniform green microstructure, high relative sintered density (99.5% theoretical density), and a nearly pore-free microstructure with an average grain size of about 1.5 μm. For the first time to our knowledge, the maximum Vickers hardness (22 GPa) was obtained for alumina simultaneously added with Mg²⁺ and EDTA, pressureless sintered at 1500°C in air.     

不同水煤浆添加剂与煤之间的相互作用规律(Ⅱ)复合煤颗粒间的相互作用对CWM表观黏度的影响

用14种不同变质程度的煤与12种分散剂成浆,测定168个CWM的表观黏度.结果表明,对同种煤,不同分散剂产生不同的分散降黏效果;对不同煤,同种分散剂的分散降黏效果也不同.通过研究CWM相对表观黏度与煤体积浓度的关系,发现Frankel方程中的k不仅与颗粒的几何分布有关,而且与煤质特性紧密相关,建立了k与煤质关系的经验方程,分析了复合煤粒间的相互作用对CWM表观黏度的影响.     

Reactivity of rice husk ash

Effect of lime:silica ratio on the kinetics of the reaction of silica with saturated lime has been investigated. Below C/S=0.65 the reaction does not proceed to completion and even in the presence of a large excess of silica only 90% lime is consumed. A parameter, lime reactivity index, has been defined to quantity the reactive silica present in rice husk ash. The product of the reaction between rice husk ash and saturated lime is a calcium hydrosilicate, CSH(I)⁷. The fibrilar structure and the hollow tubular morphology of the fibres of CSH, have been explained by a growth mechanism, where the driving force is osmotic pressure.     

Synthesis of geopolymers from volcanic ash via the alkaline fusion method: Effect of Al2O3/Na2O molar ratio of soda–volcanic ash

The alkaline fusion method was used to enhance the reactivity of volcanic ash for geopolymer synthesis. To that end, different mixtures of fused soda–volcanic ash (fused volcanic ash) were used to assess reactivity for geopolymer synthesis. The amount of amorphous phase was determined both in the volcanic ash and the fused volcanic ash and X-ray diffraction analysis was used to evaluate effect of the alkaline fusion method. Different geopolymer mortars were prepared by alkaline activation of mixtures of powders of fused volcanic ash and metakaolin and river sand using sodium silicate as activator. Metakaolin was considered as consumer of excess of alkali contained in the fused volcanic ash. The geopolymer mortars were characterized by determination of setting time, linear shrinkage, compressive strength and scanning electron microscopy. The amount of amorphous phase and excess of fused soda content of the fused volcanic ash depended on molar ratio of Al₂O₃/Na₂O and played a key role for geopolymer synthesis. The most convenient Al₂O₃/Na₂O molar ratio of fused volcanic ash to produce effective geopolymer mortars ranged between 0.13 and 0.18. This study showed that volcanic ash can be used successfully as an alternative raw material for production of geopolymers via alkaline activation of fused volcanic ash.