The direct adsorption of low concentration gallium from fly ash

This study is mainly focused on the direct adsorption of low concentration gallium from the feed solution in pre-desilication soda-lime sintering process from coal fly ash. The adsorption kinetics, mechanism, and the influence of impurities, cyclic times, and eluant content are systematically researched. Results showed that the adsorption capacity was 2.89 mg/g resin with gallium concentration of 50 mg/L. The adsorption mechanism could be explained by the interaction between the oxygen atoms and nitrogen atoms of amidoxime group. Gallium was eluted efficiently by NaOH and Na2S mixed solution and the concentration could be reached to 2400 mg/L.</p

Selective reduction leaching of vanadium and iron by oxalic acid from spent V2O5-WO3/TiO2 catalyst

Large amounts of selective catalytic reduction (SCR) denitrification catalysts with poor mechanical property are disposed and difficult to be regenerated, resulting in environmental pollution. For spent SCR denitrification catalyst, the ratio of V4+ /V5+ decreased by about 45% and Fe impurity increased &gt; 10 times, which influenced the recycling of the supporter. Selective leaching of V and Fe by oxalic acid and its reaction mechanism were investigated. Under the optimized leaching condition: oxalic acid concentration of 1.0 mol/L, reaction temperature of 90 degrees C, liquid-to-solid ratio of 20 mL/g, &lt; 75 mu m particle size and leaching time of 180 min, the leaching efficiencies of V and Fe reached over 84% and 96%, respectively. The reaction mechanism for the selective leaching of these metals was determined through UV-VIS spectrophotometry and CO2 emission analyses. After dissolution and complexation, VO2+ and Fe3+ were reduced to water-soluble cations VO2+ and Fe3+. When V and Fe was in the specific forms of VOC2O4 and Fe(C2O4)(2)(2-). at 0.33 pH, high leaching efficiency was obtained. It indicated that redox reactions led to the broken of dissolution and complexation equilibriums for VO2+, VO+ and Fe3+. For W and Ti, only dissolution and complexation reactions occurred and the leaching efficiency was limited by the solubility. The leaching residue with anatase TiO2 was recovered as carrier and used for synthesis of a new SCR catalyst.</p

Study of the V2O5-WO3/TiO2 Catalyst Synthesized from Waste Catalyst on Selective Catalytic Reduction of NOx by NH3

V2O5-WO3/TiO2 catalysts were synthesized from waste selective catalytic reduction (SCR) catalyst through oxalic acid leaching and impregnating with various V2O5 mass loadings. The denitration (deNO(x)) activity and physiochemical properties of the catalysts were investigated. All the catalysts were characterized by N-2 adsorption/desorption, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and H-2-temperature programmed reduction. The evaluation result revealed that the deNOx activity of newly synthesized catalyst with 1.0% V2O5 was almost recovered to the level of fresh catalyst, with NO conversion being recovered to 91% at 300 C-omicron, and it also showed a good resistance to SO2 and H2O. The characterization results showed that the decrease of impurities, partial recovery of the V4+/V5+ ratio, and increased reducibility were mainly responsible for the recovery of catalytic activity.</p

An Analysis Methodology for Stochastic Characteristic of Volumetric Error in Multiaxis CNC Machine Tool

Traditional approaches about error modeling and analysis of machine tool few consider the probability characteristics of the geometric error and volumetric error systematically. However, the individual geometric error measured at different points is variational and stochastic, and therefore the resultant volumetric error is aslo stochastic and uncertain. In order to address the stochastic characteristic of the volumetric error for multiaxis machine tool, a new probability analysis mathematical model of volumetric error is proposed in this paper. According to multibody system theory, a mean value analysis model for volumetric error is established with consideration of geometric errors. The probability characteristics of geometric errors are obtained by statistical analysis to the measured sample data. Based on probability statistics and stochastic process theory, the variance analysis model of volumetric error is established in matrix, which can avoid the complex mathematics operations during the direct differential. A four-axis horizontal machining center is selected as an illustration example. The analysis results can reveal the stochastic characteristic of volumetric error and are also helpful to make full use of the best workspace to reduce the random uncertainty of the volumetric error and improve the machining accuracy

Mechanism of mechanical-chemical synergistic activation for preparation of mullite ceramics from high-alumina coal fly ash

High-alumina coal fly ash (HAFA) is a special solid waste due to the existence of more than 45% alumina and 35% silica, which can be applied to prepare Al-Si series ceramics if the impurities can be removed and the Al/Si mass ratio can exceed 2.55 (Mullite: 3Al(2)O(3).2SiO(2)). In this work, a new mechanical chemical synergistic activation desilication process is proposed, and the contents of different impurities can be lowered up to less than 1%, and the Al/Si mass ratio can be elevated from 1.26 to 2.71. Especially, the mechanism of this process is investigated in detail. The analysis of the mechanism shows that the decrease of Q(4)(3Al) and the increase of Q(4)(0Al), Q(4)(1Al), and Q(4)(2Al) improve amorphous silicate reactivity through synergistic activation, and the exposed amorphous Si-O-/Si-O-Si can be removed by OH-during the desilication process (desilicated ratio &gt; 55%), which help the fine mullite to exhibit excellent properties (bulk density &gt; 2.85 g/cm(3), apparent porosity &lt; 0.5%) during the sintering process. Finally, this process not only decreases the pollution but also alleviates the shortage of Al/Si resources and promotes the clean development of coal-fired power generation

Removal of nitrides and fluorides from secondary aluminum dross by catalytic hydrolysis and its mechanism

Secondary aluminum dross (SAD) refers to hazardous waste from secondary aluminum refinement. It contains a large amount of aluminum nitride and fluorides that cause serious environmental pollution for direct discharge and hinder the resource utilization of SAD. However, it is difficult to remove nitride and fluoride simultaneously for their complicated phases. In this paper, the catalytic hydrolysis of SAD using NaOH as a catalyst to remove nitrides and fluorides synchronously was investigated systemically through single factor and response surface experiments. In addition, the chemical speciation and transformation of nitrides and fluorides were analyzed systematically. The catalytic hydrolysis removal mechanism was summarized. The optimal conditions for catalytic hydrolysis were established as follows: reaction temperature 96.60 °C; reaction time 2.85 h; liquid-solid ratio 9.28 mL/g and catalyst addition 12.62 wt %; and removal efficiency of nitrides and fluorides reached 99.03% and 81.93%, respectively. The mechanism of nitrides removal was that aluminum nitride was hydrolyzed to Al(OH)3 and NH3. NaOH reacting with Al(OH)3 covering on the surface of AlN and the rapid escape of NH3 promoted the hydrolysis of AlN under the catalysis of NaOH. The mechanism of fluorides removal was that the encapsulated fluoride particles were opened by catalytic hydrolysis to be dissolved in the solution. In this research, nitrides and fluorides were removed efficiently and synchronously. The hydrolysis residues can be used to prepare polyaluminum chloride (PAC) and ceramic materials. The hydrolysate can be prepared NH3·H2O by evaporative in alkaline solution. Then the solution without NH4+ was prepared Al(OH)3 by precipitation of adjusting pH value using HCl. And the remained liquid after removing NaAlO2 was used to prepare refining agent by evaporative crystallization. The work in this paper was beneficial for the utilization of SAD

Recovery of tungsten and titanium from spent SCR catalyst by sulfuric acid leaching process

The widespread use of selective catalytic reduction (SCR) catalysts has resulted in a large accumulation of spent SCR catalysts. These spent catalysts present a significant risk of environmental hazards and potential for resource recovery. This paper presents a feasible process, which works using atmospheric pressure leaching, of tungsten and titanium recovery from spent SCR catalysts. In this new method, titanium and tungsten are simultaneously leached with sulfuric acid as the leaching agent. After hydrolysis and calcination, titanium-tungsten powder with low impurity and reconstructed pore properties was obtained. The optimal conditions for the leaching of Ti and W were as follows: temperature, 150 degrees C; reaction time, 60 min; H2SO4 concentration, 80 %; mass ratio of H2SO4/TiO2, 3:1; and diluted H2SO4 concentration, 20 % after reaction. With these optimum conditions, the leaching efficiency of Ti and W were found to be 95.92 % and 93.83 %, respectively. The ion speciation and reaction mechanism of W were studied by Raman spectroscopy, FTIR, and UV-vis. The formation of heteropolytungstate with a Keggin structure is essential for the synergistic leaching of Ti and W, as the heteropolytungstate can be stably dissolved in the acid solution. During the hydrolysis process, heteropolytungstate gradually decomposed into Ti4+ and WO42- due to the formation of insoluble Ti(OH)(4) from Ti4+ in the solution. This study demonstrated an effective method for synergistic recovery of titanium and tungsten from the spent SCR catalyst

Simultaneous removal of SO2 and NOx from flue gas using (NH4)(2)S2O3/steel slag slurry combined with ozone oxidation

The use of thiosulfate salt (S2O32-), a low-cost reductant, as an absorbent for NO2 removal has been rarely reported. In this study, we propose a method that combines ozone oxidation and (NH4)(2)S2O3/steel slag slurry spraying to simultaneously remove sulfur dioxide (SO2) and nitrogen oxides (NOx) from flue gas. We investigated the effects of operation conditions on the simultaneous removal efficiencies of SO2 and NOx. Results showed that SO2 removal efficiency was affected by pH, whereas NOx removal efficiency was mostly influenced by (NH4)(2)S2O3 concentration, reaction temperature, and pH level. Under optimal operation conditions, removal efficiencies of almost 100% for SO2 and above 78.0% for NOx were achieved. NH4+ in the steel slag slurry could tolerate high NO2- concentrations (up to 3.00 mol/L), and the co-existence of NH4+ and S2O32- had a significant synergistic effect on NOx removal. Together with S2O32-, Mg2+ that leached from the steel slag also had a synergistic effect on NO2 removal. We established the reaction mechanisms for NOx removal using (NH4)(2)S2O3/steel slag slurry. In this process, S2O32- acted as a reducing agent and an oxidation inhibitor of SO32-, thereby enhancing NO2 removal. Moreover, NH4+ inhibited the denitration product (NO2-) from decomposing into NO and NO2, thereby accelerating NOx removal

Recovery of tungsten and titanium from spent SCR catalyst by sulfuric acid leaching process

The widespread use of selective catalytic reduction (SCR) catalysts has resulted in a large accumulation of spent SCR catalysts. These spent catalysts present a significant risk of environmental hazards and potential for resource recovery. This paper presents a feasible process, which works using atmospheric pressure leaching, of tungsten and titanium recovery from spent SCR catalysts. In this new method, titanium and tungsten are simultaneously leached with sulfuric acid as the leaching agent. After hydrolysis and calcination, titanium-tungsten powder with low impurity and reconstructed pore properties was obtained. The optimal conditions for the leaching of Ti and W were as follows: temperature, 150 degrees C; reaction time, 60 min; H2SO4 concentration, 80 %; mass ratio of H2SO4/TiO2, 3:1; and diluted H2SO4 concentration, 20 % after reaction. With these optimum conditions, the leaching efficiency of Ti and W were found to be 95.92 % and 93.83 %, respectively. The ion speciation and reaction mechanism of W were studied by Raman spectroscopy, FTIR, and UV-vis. The formation of heteropolytungstate with a Keggin structure is essential for the synergistic leaching of Ti and W, as the heteropolytungstate can be stably dissolved in the acid solution. During the hydrolysis process, heteropolytungstate gradually decomposed into Ti4+ and WO42- due to the formation of insoluble Ti(OH)(4) from Ti4+ in the solution. This study demonstrated an effective method for synergistic recovery of titanium and tungsten from the spent SCR catalyst

Synthesis of Calcium Silicate Hydrate in Highly Alkaline System

Synthesis of calcium silicate hydrate (C-S-H) was conducted over the range of 50 degrees C-90 degrees C and C/S ratio of 0.86-2.14 in the highly alkaline Na2O-CaO-SiO2-H2O system for silicon utilization in high alumina fly ash. Structural change in C-S-H formed in the highly alkaline system was investigated using XRD and Si-29 MAS NMR spectra. X-ray photoelectron spectroscopy was used to confirm the amount of sodium ions in C-S-H. Conversion of Si may reach 99% under optimum conditions. A higher degree of polymerization of silicate was obtained at lower temperature and C/S ratio. Na+ was confirmed to exist as Na-OSi and Na-OH. The amount of Na+ is the least at C/S ratio of 1.43, which conform to the prediction of topological constraint theory. High Ca/Si ratio leads to the increasing in Na+ combined in the interlayer. Increasing in the Na+ concentration in the system also increases the amount of Na+ combined in the interlayer and reduces the polymerization. Ion exchange was proven to be an effective way to remove Na+ combined in the interlayer of C-S-H.</p