Formation Of Aluminosilicates Research Articles

Study on the Characteristics of Crystal Formation and Transformation of Alkali-Activated Slag Minerals Induced by Weak Alkali

Strong-alkali activation is a prerequisite needed to ensure the full polymerization activity of alkali slag binder and establish excellent mechanical properties; however, it substantially increases the preparation cost. In this study, the effects of both strong and weak alkaline activators on the activation performance of alkali slag were examined, using a combination of X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy analysis methods. The reaction mechanism was analyzed under different alkaline conditions, and the preparation cost could be significantly reduced without significantly degrading mechanical properties. The results indicate that Ca(OH)2 can stimulate the reactivity of slag, resulting in a 40% decrease in compressive strength (compared to NaOH) but a 25–50% reduction in preparation cost. With increasing Ca(OH)2 dosage, the compressive strength first increases and then decreases. The best excitation effect is achieved at a dosage of 40 g Ca(OH)2 per 450 g GBFS. The formation of aluminosilicate is the main driving force for the observed increase in compressive strength. Excessive dosage of Ca(OH)2 will lead to its deposition in the specimen, thus affecting the development of compressive strength.

The synergistic role of sludge conditioner FeCl3/Rice husk on co-combustion with coal gangue: Thermaldynamic behavior, gases pollutants control and bottom ash stabilization

Coal processing invariably generates substantial quantities of low calorific value waste, specifically coal gangue (CG), which can be advantageously utilized by combusting to yield valuable electrical energy. However, CG incur poor ignition and flame instability, and consequently is not suited to separate combustion. The co-combustion with sewage sludge (SS) has demonstrated positive impacts on energy recovery, whereas the SS dewatering may significantly influence the co-combustion behavior. Therefore, this study systematically investigated the impact of two typical sludge conditioner, namely FeCl3·6H2O and rice husk (RH), which functions as flocculant and skeletal builder, on their synergistic role on co-combustion with CG. The thermal dynamic combustion behavior, pollutant emissions, slag tendency and bottom ash stability and toxicity were systematically studied. A robust positive synergism is observed, attributed to heat compensation and the formation of alkali metal aluminosilicates from Rh during the ignition phase. Concurrently, the temperature dependent iron oxides evolution enhances the acceleration of O2 loop, thereby promoting the char combustion. After being jointly conditioned with Rh and FeCl3, the co-combustion with CG resulted in CCi being 3.46 times higher than that of C1S3, and the average activation energy in each stage was reduced by 49.1 %. Significantly, the sludge conditioner also contributes to the reduced exhausted gases such as CO2, SO2 and NO. The Rh in SS has been found to mitigate slagging and fouling tendencies, while the retention of Cr, Cu, Ni, and Pb is greatly improved due to the stabilization of silicate minerals in CG. The Artificial Neural Network (ANN) models were established to predict the thermogravimetric experimental data of CG-SS-Rh/Fe, which aims to provide a basis for the selection of optimal operating conditions in real industrial applications.

Advances in using seawater in slag-containing cement systems

The use of seawater as mixing water in concrete is motivated by an increasing danger of freshwater shortages. The factors restricting its use in concrete include a high risk of concrete structure degradation as well as steel reinforcement corrosion initiated by the chlorides and sulphates in seawater. The objective of this study is to evaluate the potential of ternary cementitious systems containing the substitution of a clinker constituent in cements with ground granulated blast furnace slag (GGBFS) at rate of 45 wt% and 85 wt% and zeolite (10 wt%) mixed with seawater. Moreover, the effects of alkaline activators were evaluated as a potential method to compensate the low strength of high volume slag-zeolite-cement systems containing seawater. The hydration process was evaluated by means of calorimetry, X-ray diffraction (XRD) and scanning electron microscopy (SEM), and was supplemented by the compressive strength development (2, 7, 28 days) evaluation. It was found that presence of GGBFS in seawater-mixed systems, promotes an increase in the volume of low-calcium silicate hydrate gel-like phases, which (in addition to the layered double hydroxide phases) bind the Cl-- and SO42--ions of seawater. However, at high volume replacement level (85 wt%) the accelerating effect of seawater is limited resulting in slow rate of concrete strength gain. The proposed alkaline activation, allowed the strength enhancement, but also satisfied the conditions for the complete binding of Cl-- and SO42− -ions, due to the formation of zeolite-like alkaline aluminosilicate hydrates in the resultant cement matrix. It was found that the addition of natural zeolite accelerates hydration reactions and crystallization processes in cement systems. As an outcome, due to synergistic effect of seawater and alkali-activation, the proposed ternary blend containing 5 wt% of Portland cement exhibited only 24 % lower 28 days compressive strength when compared to freshwater-mixed Portland cement (90 wt%) – zeolite (10 wt%) reference mix.

Durability of Non-Heat-Cured Geopolymer Mortars Containing Metakaolin and Ground Granulated Blast Furnace Slag

This study presents the durability, strength and microstructure of non-heat-cured geopolymer mortars (GMs) containing metakaolin (MK), ground granulated blast furnace slag (GGBFS), potassium hydroxide (KOH), sodium metasilicate (Na2SiO3), CEN sand and network water. Optimum MK, GGBFS and activator solution ratios were investigated, and the compressive strength of non-heat-cured 28-day GMs reached 55 MPa. Analysis of GMs using scanning electron microscopy (SEM), energy-dispersive X-ray spectrophotometry (EDX) and X-ray powder diffraction (XRD) revealed alumino-silicate formation, potassium from KOH solution and calcium from GGBFS. It showed that the grains containing high silica in the form of quartz crystals were found in the gel formation. The strength and durability of MK- and GGBFS-based GMs exposed to freeze–thawing, a high temperature, wear loss, magnesium sulfate (MgSO4), sodium sulfate (Na2SO4) and HCl solutions were found to be sufficient.

Structure characteristics and combustion kinetics of the co-pyrolytic char of rice straw and coal gangue

Co-combustion is a technology that enables the simultaneous and efficient utilization of biomass and coal gangue (CG). Nevertheless, the factors that affect the combustibility of co-pyrolytic char, which represents the rate-determining step of the entire co-combustion process, remain unclear. This study investigates the impact of the physicochemical properties of co-pyrolytic char, including pore structure, carbon structure, and alkali metals, on the combustion characteristics. The TGA analysis indicates that the ignition and burnout temperatures of the co-pyrolytic char increase as the CG mixing ratio increases, resulting in a prolonged combustion. This is due to the fact that the carbon structure of the co-pyrolytic char becomes increasingly aromatic, accompanied by a reduction in aliphatic hydrocarbons and oxygen-containing groups as the CG mixing ratio increases. Furthermore, the high ash content of the CG is another significant factor contributing to the observed reduction in combustibility. The reaction between mullite, quartz in CG, and alkali metals in biomass results in the formation of aluminosilicate, which reduces the catalytic ability of alkali metals. Furthermore, the char combustion kinetics are analyzed by the KAS method, and the results indicate that the introduction of CG increases the activation energy of the entire char combustion process. The activation energy of the 80RS20CG is within the range of 102.22–164.99 kJ/mol, while the RS char is within the range of 89.87–144.67 kJ/mol.

Concurrent arsenic, fluoride, and hydrated silica removal from deep well water by electrocoagulation: Comparison of sacrificial anodes (Al, Fe, and Al–Fe)

Some studies have reported the removal of As (As) and fluoride (F−) using different sacrificial anodes; however, they have been tested with a synthetic solution in a batch system without hydrated silica (SiO2) interaction. Due to the above, concurrent removal of As, F−, and SiO2 from natural deep well water was evaluated (initial concentration: 35.5 μg L−1 As, 1.1 mg L−1F−, 147 mg L−1 SiO2, pH 8.6, and conductivity 1024 μS cm−1), by electrocoagulation (EC) process in continuous mode comparing three different configurations of sacrificial anodes (Al, Fe, and Al–Fe). EC was performed in a new reactor equipped with a small flow distributor and turbulence promoter at the entrance of the first channel to homogenize the flow. The best removal was found at j = 5 mA cm−2 and u = 1.3 cm s−1, obtaining arsenic residual concentrations (CAs) of 1.33, 0.45, and 0.77 μg L−1, fluoride residual concentration (CF−) of 0.221, 0.495, and 0.622 mg L−1, and hydrated silica residual concentration (CSiO2) of 21, 34, and 56 mg L−1, with costs of approximately 0.304, 0.198, and 0.228 USD m−3 for the Al, Fe and Al–Fe anodes, respectively. Al anode outperforms Fe and Al–Fe anodes in concurrently removing As, F− and SiO2. The residual concentrations of As and F− complied with the recommendations of the World Health Organization (WHO) (As < 10 μg L−1 and F− < 1 mg L−1). The spectroscopic analyses of the Al, Fe, and Al–Fe aggregates showed the formation of aluminosilicates, iron oxyhydroxides and oxides, and calcium and sodium silicates involved in removing As, F−, and SiO2. It is concluded that Al would serve as the most suitable sacrificial anode.

Effect of Deashing Treatment on Ash Fusion Characteristics of Biochar from Bamboo Shoot Shells.

To investigate the influence of deashing on fusion characteristics, a combined method of water and acid washing with different sequences (water washing followed by acid washing, and acid washing followed by water washing) was used to treat the biochar of bamboo shoot shells (BBSSs). The results show that deashing decreased the K content of the biochar from 50.3% to 1.08% but increased the Si content from 33.48% to 89.15%. The formation of silicates and aluminosilicates from alkali metal oxides with silicon was an inevitable result of ash phase transformation at the high temperatures used to improve the fusion temperature (>1450 °C). The thermochemical behavior of ash mainly occurs at 1000 °C. The deashing treatment significantly reduced the reaction intensity during the high-temperature process. This significantly increased the thermal stability of the ash. The adjustment of the washing sequence had a slight impact on the chemical compositions, but the differences in ash micromorphology were obvious. Deashing treatments with different washing sequences can significantly improve ash fusion properties effectively and reduce the risk of scaling, slagging, and corrosion. This study provides a new and reasonable strategy for the deashing of biochar to commercially utilize bamboo shoot shell resources.

Alkali thermal fusion: A prospective route to enhance the reactivity of low-grade clay and utilize as supplementary cementitious material (SCM)

Common clay deposits contain a variety of minerals that provide low and unpredictable reactivity even after calcination. This study aims to enhance the reactivity of such low-grade clay via alkali thermal fusion, where clay was co-calcined with different dosages of NaOH to achieve superior reactivity. The effects of such co-calcination on the formation of reactive aluminosilicates were monitored using high-temperature in-situ X-ray Diffraction (XRD). Additionally, the role of different alkali dosages on the characteristics of the calcined clays was studied using ex-situ XRD, FTIR, ICP-OES, and 29Si NMR. The co-calcination process significantly enhanced the Al and Si dissolution from the calcined clays, which subsequently improved their pozzolanic properties. All of the alkali-fused SCMs satisfied the modified strength activity index (SAI) requirement and the lower dosages of alkali-containing samples (5 % NaOH) showed 50 % reduction in expansion due to alkali silica reaction.

Shrinkage in low-calcium fly ash geopolymers for precast applications: Reaction product content and pore structure under drying conditions

Shrinkage and strength gain in alkali-activated low-calcium fly ash (AAF) geopolymers are evaluated. AAF mixtures that are proportioned for strength are evaluated for typical variation of compositional variables including water and sodium contents in the mixture. Strength gain in the AAF mixture is related with the formation of the sodium aluminosilicate (NASH) gel under accelerated curing conditions. Moisture loss produced by drying results in an overall reduction in the NASH gel content formed in the AAF, while its composition is not changed. NASH content is higher in AAF with lower water content producing finer pore structure and higher strength. The excess Na does not participate in NASH formation; however, the excess Na is available like a filler, which does not contribute to the strength of the AAF while producing pore refinement. Shrinkage produced on drying depends on the water and sodium contents in the activated paste. AAF mixture made with smaller water content has a refined pore structure, which results in increased shrinkage strain on drying while the mass loss is lower. Excess sodium in AAF produces a larger shrinkage strain on drying due to the pore refinement. AAF mixtures with a low sodium content and prevention of moisture loss during strength gain is suggested for precast applications.

Construction ceramsite from low-silicon red mud: Design, preparation, and sintering mechanism analysis

Low-silicon red mud (LSRM) is limited in its application in the field of light aggregates for construction. Supplementation sintering materials (SSMs) effectively aids LSRM in preparing sintered construction ceramsite. To produce an LSRM-based ceramsite with economical and effective performance, this study investigated the effect of SSMs (silica fume, bentonite, and glass powder) on the performance of the ceramsite and determined the optimum ratio using the response surface method (RSM). The results indicated that the silica fume (SF) significantly influenced the apparent density (AD) and water absorption (WA) of the ceramsite; with an increase in SF, AD increased and WA decreased. SF and glass powder (GP) were negatively correlated with particle strength (PS), whereas bentonite was positively correlated with PS. The optimum doping values for SF, bentonite, and GP were determined as 19.79, 9.28, and 12 wt%, respectively. Ceramsite could achieve the best performance with an AD of 1254 kg/m3, a WA of 3.13%, and a PS of 13.1 MPa. In addition, the formation of aluminosilicate played a positive role in the fixation of heavy metals and the reduction of the pH value of ceramsite, ensuring its good environmental performance.

Electrocoagulation with Fe-Al hybrid electrodes for the removal of arsenic, fluoride, and silica from natural groundwater

This communication is about the removal of arsenic (As), fluoride (F−) and hydrated silica (HS) from real underground water (initial concentration: 28 µg L−1 arsenic, 1.55 mg L−1F−, 155 mg L−1 HS, 35 mg L−1 sulfate, pH 7.4, and 470 µS cm−1 conductivity) by electrocoagulation (EC). The novel EC reactor consists of eight horizontally stacked cells using Fe and Al plates as sacrificial anodes with an upward flow. The abatement of As and the elimination at the same time of F− and HS was performed by analyzing the influence of the mean linear flow velocity (1.2 < u < 4.8 cm s−1) at different current densities (3 < j < 7 mA cm−2) imposed on the EC system. The best condition was carried out at j = 7 mA cm−2 and u = 1.2 cm s−1, achieving complete arsenic elimination, and a remaining F− concentration of 0.45 mg L−1, fulfilling the World Health Organization (WHO) guideline for arsenic (< 10 μg L−1) and fluoride (< 1.5 mg L−1). The remaining HS reached a value of 10 mg L−1. Spectroscopic techniques applied to the Fe-Al flocs evidenced the generation of iron oxides and hydroxides, as well as the formation of aluminosilicates.

Preparation of drilling cuttings-coal fly ash based ceramic proppants: The roles of barite

This study presents the feasibility of preparing ceramic proppants (CPs) using drilling cuttings (DCs) and coal fly ash (CFA) via high-temperature sintering. The reaction behavior of barite in ceramic proppant precursors originating from DCs during the sintering process was investigated. The breakage ratio of the CPs (optimal group S3) met the requirements of Chinese standard SY/T 5108-2014 (2 K grade). The primary chemical reactions (7–8 in Table 4) between the barite and silica/alumina components resulted in a reduction of the eutectic point of the mixtures and the formation of aluminosilicates containing barium. However, these interactions also released gases (SO2 and O2), which created pores and weakened the CPs strength. The ideal temperature range for sintering is between 1170 and 1200 °C, during which there should be a gradual weight loss and minimal gas generation. This range will also ensure that the appropriate amount of liquid phase is present, which will have a moderate viscosity and aid in the densification of the ceramic proppants, as well as the formation of a dense enamel layer. The composite reactions of barite in the S3 sample follow a one-and-a-half-order chemical reaction mechanism within the temperature range of 950–1200 °C. The average activation energy and pre-exponential factor were 583.304 kJ mol−1 and 5.81 × 1020 min−1, respectively. The kinetic and reaction rate equations for the composite reactions were (1 − α)−1/2–1 = (5.81 × 1020 × e−5.83 × 10^5/RT) × t and dα/dt = (2(1 − α)3/2) × (5.81 × 1020 × e−(5.83 × 10^5)/RT)), respectively. This study provides a theoretical basis and guidelines for large-scale production of CPs using DCs and CFA.

Ascertaining the Si-substitution on the tribo-corrosion behaviors of Ti3AlC2 in molten Solar Salt

As a promising working medium for thermal transportation, nitrate-based molten salts are widely adopted for current concentrating solar power (CSP) plants. However, their corrosive nature also brings severe safety hazards to the system, e.g., the impellers and cover in molten salt pumps. To study the potential application of MAX ceramics as a proactive coating for these parts, tribo-corrosion behaviors of Ti3AlC2 and its Si-substituted analogs against GCr15 steels are evaluated in the molten Solar Salt at 300 °C to simulate the operating condition of the cold-salt pump. The Si-substituted MAXs present higher anti-wear performance than pristine Ti3AlC2. With an optimal composition of Ti3Al0.6Si0.4C2, about a 25% reduction in mean wear rate to that of Ti3AlC2 is achieved. Through a comprehensive analysis of the morphological and chemical states of both tribo-corroded and static corroded surface, the effects of Si on the tribo-corrosion behaviors of Ti3AlC2 is illuminated. The enhanced performance after Si addition is ascribed to the facilitated formation of aluminosilicates as corrosion products on the surface, which act as a lubricant as well as impeding the dissolution of Al into the molten Solar Salt.

Effects of torrefaction on ash-related issues during biomass combustion and co-combustion with coal. Part 3: Ash slagging behavior

Torrefaction is a competitive technology for biomass upgrading. Knowing that the effects of torrefaction on ash-related issues during biomass combustion and co-combustion with coal have been less investigated, Parts Ⅰ and Ⅱ of this work investigated the particulate matter emission and ash fouling behavior. To be a continuation, in the present paper, the effect of biomass torrefaction on ash slagging deposition which occurs in the high-temperature areas of the furnace was focused on. Two herbaceous biomass, one woody biomass, and their torrefied chars were fired and co-fired with two coals respectively on a drop-tube furnace at 1300℃. The slags were collected from mullite tubes placed in the furnace for quantification and characterization. Computer-controlled scanning electron microscope (CCSEM) was employed to obtain the distribution of particle size and inorganic species in the bulk ash. The results indicate that co-firing the biomass with high-Ca coal significantly reduces the ash slagging rates due to the substitution of alkalis by Ca from the silicates/aluminosilicates which inhibits the agglomeration and sintering of the ash particles, and finally reduces the inertial impaction and capture of the particles on the tube. Co-firing corn stalk with the high-Si/Al coal promotes the formation of alkaline aluminosilicates which are sticky at a high temperature. Therefore, the slagging tendency is exacerbated. Torrefaction reduces the ash slagging rate of sawdust resulting from the effective removal of S and Cl and the transformation of AAEMs (alkaline and alkaline earth metals) into less-reactive forms during torrefaction which reduces the vaporization and transformation of AAEMs into coarse particles as aluminosilicates by surface reactions. However, the ash slagging rates are increased by torrefaction for other fuels due to more retention of AAEMs after torrefaction resulting in more mixed silicates or aluminosilicates in bulk ash contributing to the growth of slagging deposits during combustion. Measures are suggested to be taken, such as optimizing the operation conditions, co-firing with high-Ca coals, using additives, etc. to alleviate the ash slagging during torrefied herbaceous biomass combustion.

Effects of torrefaction on ash-related issues during biomass combustion and co-combustion with coal. Part 2: Ash fouling behavior

Torrefaction is a promising pretreatment technology that allows the utilization of biomass on large scales. This work provides new knowledge regarding the effects of torrefaction on ash fouling during biomass combustion and co-combustion by correlating them to element repartitioning due to torrefaction, which has little been evaluated in the literature. Two herbaceous biomasses (rice husk and corn stalk) and one woody biomass (sawdust) were torrefied on a fixed bed at 270℃ in N2. The raw and torrefied biomass were fired and co-fired with two coals on a drop-tube furnace at 1300℃ in air. The samples were characterized by various techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, and ion chromatography. The results show that the fuel interactions during co-combustion inhibit the formation of inside fouling while the incorporation of alkalis in the aluminosilicates promotes the growth of outside deposits. Torrefaction reduces the formation of chlorides and sulfates during combustion directly and consequently inhibits the inside deposition due to the fractional removal of Cl, S, and alkalis in biomass. Besides, the less condensation of chlorides/sulfates on the surface of the tube and the coarse particles tend to reduce the formation and growth of the outside deposits. However, the elemental repartitioning during torrefaction leads to more retention of alkalis which can aggravate the formation of mixed aluminosilicates during combustion and favors the outside deposition. Both co-combustion and biomass torrefaction have the potential to decrease the ash fouling tendency during biomass combustion considering that they reduce the inside fouling deposits which are problematic in practice. Based on the ash composition of the fuels, a modified fouling index [soluble (Na2O + MgO + K2O + CaO)] * [SiO2/(SiO2 + Al2O3)] is proposed which shows a superior linear correlation with the inside fouling rates of the various fuels investigated, indicating its feasibility for prediction of the ash fouling tendency.

Distribution, risk assessment and stabilization of heavy metals in supercritical water gasification of oily sludge

Supercritical water gasification (SCWG) of oily sludge is a potential handling method for resource utilization and pollution reduction. Heavy metals (HMs) in oily sludge were assessed due to their threat to human health and environmental safety. This work investigated the distribution of four HMs (Cu, Zn, Ni and Cr) under different reaction conditions (550–700 °C, 1–60 min). The concentrations of HMs in liquid residues (LRs) decreased continuously at higher temperatures and longer residence times except for Ni. Besides, the concentrations of HMs in solid residues (SRs) increased after SCWG except for Zn, and they varied slightly under different conditions. Then, HMs in LRs and SRs were evaluated in terms of Nemerow index, geo-accumulation index and potential ecological risk. The results indicated that the pollution risks of HMs in LRs were minimum at 650 °C and 30 min, while that in SRs changed little. When Na2CO3 was added, pollution risks changed slightly, but nearly complete stabilizations of Cu, Zn and Cr (96.2%, 84.2% and 98.6%) were achieved at 600 °C. Adding Na2CO3 promoted the formation of aluminosilicate to combine with HMs and enhanced their stabilization notably. This work may demonstrate a promising clean way for oily sludge utilization and HMs stabilizing.

Synthesis of ternary binders and sand-binder ratio on the mechanical and microstructural properties of geopolymer foamed concrete

The development of sustainable construction building materials with a lower environmental impact throughout both the manufacturing and operation phases of the material lifecycle is capturing the attention of the global housing and construction sectors. Recent advancements have resulted in the development of geopolymer foam concrete, which combines the performance and energy savings associated with lightweight foam concrete with the cradle-to-grave emissions reductions associated with the use of a geopolymer binder composed of supplementary cementitious materials (by-products). The purpose of this study is to determine the influence of sand to binder ratio and by-product materials, fly ash, ground granulated blast furnace slag, palm oil fuel ash, palm oil clinker powder and bottom ash on structural grade geopolymer foamed concrete with a density of 1700 kg/m3. The mechanical properties such as compressive strength, splitting tensile strength, rupture modules, and static and dynamic modules of elasticity were investigated; microstructure investigations using X-ray Diffraction (XRD) and Field-Emission Scanning Electron Microscope (FESEM) were also reported. The results show that geopolymer foamed concrete (GFC) with a structural grade concrete of compressive strengths ranging from 27 to 39 MPa could be produced. The use of fine sand improved the geopolymer foamed concrete's mechanical and microstructural characteristics. The tensile strength, modulus of rupture, and elasticity modulus were found in the ranges of 0.9 – 2.53 MPa, 1.35 – 4.28 MPa, and 3.54 – 6.86 GPa, respectively. The non-uniform distribution of the voids of ternary composites geopolymer foamed concrete and the formation of calcium aluminosilicate hydrates C-(N-) A-S-H gel are found.

Experimental and theoretical studies on the adsorption performance of lead by thermal pre-activation and phosphate modified kaolin sorbent

Lead removal from flue gas continues to be an important environmental issue. Adding sorbents in the furnace is a reliable method to control lead emission. Modified kaolin sorbent developed by a combined method of thermal pre-activation and phosphate impregnation was first applied to capture lead from flue gas. Modified kaolin exhibited higher PbCl2 removal performance than raw kaolin at 800–1100 ℃. The best adsorption performance of raw and modified kaolin was obtained at 1000 ℃ with adsorption efficiencies of 76.72 % and 85.87 %, respectively. The adsorption capacity of modified kaolin was about 283.51 mg/g at 1000 ℃. Lead aluminosilicate and lead phosphate were produced in the adsorption reaction. O2 was conducive to the conversion of PbCl2 to PbO, and directly participated in the formation of lead aluminosilicate· H2O was in favor of the adsorption reaction, and reduced the energy barrier for dechlorination of PbCl2, and promoted the eutectic melting process. SO2 and NO inhibited PbCl2 removal due to the competitive adsorption between SO2/NO and PbCl2 at the active sites. High concentration of HCl can obviously suppress the reaction of PbCl2 and modified kaolin. Quantum chemistry calculations were conducted to identify the active sites, and to uncover the molecular-level interaction of PbCl2 and modified kaolin. Theoretical results manifested that PbCl2 adsorption was chemisorbed on kaolin (001) surface. The adsorption energies of PbCl2 on raw kaolin and modified kaolin were − 124.60 and − 205.90 kJ/mol, respectively. Al, O and P atoms of modified kaolin were identified as the active sites for PbCl2 adsorption.

Simultaneous removal of arsenic, fluoride, and hydrated silica from deep well water by electrocoagulation using hybrid Al-Fe electrodes

This paper deals with the simultaneous removal of arsenic, fluoride, and hydrated silica (HSi) from natural deep well water (26 µg L−1 As, 1.65 mg L−1F−, 160 mg L−1 HSi, 0.3 mg L−1PO43−, pH 7.5, and conductivity 450 µS cm−1) by electrocoagulation (EC). An up-flow EC reactor made up of an eight-cell stack using aluminum and iron plates as sacrificial electrodes in horizontal mode was used. The influence of the mean linear flow velocity (1.2 <u < 4.8 cm s−1) and current density (3 < j < 5 mA cm−2) applied to the EC reactor on the removal efficiency of As, F−and HSi was systematically examined. The best electrocoagulation trial was obtained at j = 5 mA cm−2 and u = 1.2 cm s−1, producing an aluminum and iron coagulant dose of 33.73 and 68.4 mg L−1, respectively, attaining residual concentrations of arsenic (CAs = 0.02 μg L−1) and fluoride (CF− = 0.88 mg L−1) below the World Health Organization (WHO) guideline (As < 10 μg L−1 and F− < 1.5 mg L−1). The residual HSi concentration was CHSi = 33 mg L−1, with electrolytic energy consumption and total operating cost of EC of 2.07 KWh m−3 and 0.29 USD m−3, respectively. The SEM-EDS, FXRD, XRD, FTIR, and Raman analyses of the Al-Fe flocs evidence the formation of iron silicates and aluminosilicates formed by the reaction between iron and aluminum with silica, respectively, and the existence of iron oxides and iron oxyhydroxides. The arsenic was removed by adsorption on aluminum and iron aggregates, while fluoride substitutes a hydroxyl from aluminum flocs.

Phase diagram for hydrothermal alkali activation of kaolin and quartz: Optimal digestion for the synthesis of zeolites

Low-temperature activation of quartz and kaolin, two of the most abundant and affordable raw materials as the sources of alumina and silica for the production of zeolites, is highly desirable but is hampered by several challenges such as incomplete activation and the formation of acid-resistant aluminosilicates. In this paper, the hydrothermal alkali activation processes of kaolin and quartz with different Si/Al ratios have been studied in detail, aiming to establish a phase diagram for the optimal digestion of silica and alumina. The effects of the Si/Al ratio, reaction time, reaction temperature, alkali concentration, and doses of hydrothermal alkali activation have been thoroughly investigated and optimized. Sodalite, hydroxycancrinite and analcime are found to be the dominant aluminosilicates as activation products. This is the first demonstration that the molar ratio of NaOH/(Si + Al) is the key factor in controlling the formation of aluminosilicates. The establishment of this phase diagram allows us to avoid the formation of troublesome analcime, and it can be used for effectively converting most natural aluminosilicate materials into sol-gel as platform chemicals for the synthesis of zeolites and other aluminosilicate derivatives.