煅烧-碱浸法从钒铬还原渣中分离回收钒铬

通过煅烧-碱浸法从钒铬还原渣中分离回收钒铬,考察了煅烧反应过程并探讨了煅烧-碱浸条件对浸出钒的影响。结果表明：煅烧过程中Cr（Ⅲ）和V（Ⅳ） 反应生成中间产物CrVO₄,随后CrVO₄分解为Cr₂O₃和V₂O₅;相同浓度条件下,在V₂O₅浸出效果方面NaOH要优于Na₂CO₃,提高浸出介质浓度和延长浸出时间有利于V₂O₅的浸出,而浸出温度对V₂O₅浸出无明显影响,钒铬还原渣在850℃煅烧1.5 h后经3 mol·L^-1 NaOH在90℃浸出1.5 h,滤渣中的Cr₂O₃质量分数高于96%,钒、铬的浸出率分别为87.3%和小于1%,另外,利用酸性铵盐法能够沉淀滤液中97%的钒。     

Surface and structure characteristics of commercial K-Feldspar powders: Effects of temperature and leaching media

This study presents morphological and structural variations of K-Feldspar mineral after acid treatment. Both organic and inorganic acids such as C₂H₂O₄, HCl, HNO₃ and H₂SO₄ were employed for this purpose. Another aim of this study was to find an optimum experimental condition for iron (Fe) removal with a minimum damage on the structure of K-Feldspar in which high whiteness index is obtained. The effect of different parameters such as concentration, pH and temperature on the final structure of this mineral was investigated. To find out the chemical composition of powder, XRF was utilized. FTIR, XRD and SEM were employed to study the structure of mineral. Spectrophotometry was chosen to analyze whiteness index of powder after acid treatment. It was found that O—Al—O bond at 647 cm^-1 for H₂SO₄ and HNO₃ treated sample disappeared. However, HCl and C₂H₂O₄ were ineffective at this band. In addition, the results revealed an increase in K-Feldspar content, a decrease in Fe content, an increase in whiteness index and no significant structural change for C₂H₂O₄ leached sample. Whiteness index of 91% was obtained for C₂H₂O₄ leached sample with the pH of 2.5 to 3 at temperature of 50℃ and during 1 h.     

Adsorption of difenzoquat on montmorillonite: model calculations and increase in hydrophobicity

The adsorption of difenzoquat (DZ) on montmorillonite was studied at a wide range of concentrations and ionic strengths. Up to difenzoquat loadings of 0.4 mmol/g clay, all the added cation were adsorbed. Maximal adsorbed amounts exceeded slightly the cation exchange capacity (CEC) of the clay (0.8 mol_c/kg). The adsorbed amounts did not change upon increasing the concentration of NaCl in the medium to 500 mM. An adsorption model that combines electrostatic equations with specific binding in a closed system could adequately predict the adsorbed amounts of DZ, even at high ionic strength. Simultaneous adsorption of the divalent cationic herbicide diquat (DQ) and DZ was also determined and the predictions of the model were adequate for total loadings up to the CEC of the clay. At higher loads the model adequately predicts the DZ adsorbed, but underestimates the amounts of DQ adsorbed. The influence of adsorbed DZ on the hydrophobicity of montmorillonite was tested by using the hydrophobic herbicide pendimethalin (PM). The adsorption isotherm of PM on crude montmorillonite is of the S type, indicating very low adsorption at low added amounts, and increasing affinity after part of the surface is covered with the hydrophobic molecules. Adsorption of PM on montmorillonite saturated with DZ up to 80% of the CEC showed a C behavior, indicating a partition mechanism between the solvent and the adsorbent even at low added amounts. The enhanced hydrophobicity of DZ–montmorillonite was also demonstrated in qualitative experiments in a mixed chloroform–water environment: whereas the crude clay mineral stayed in the water phase, DZ–montmorillonite concentrated in the chloroform phase.     

Preparation of high-purity graphite from a fine microcrystalline graphite concentrate: Effect of alkali roasting pre-treatment and acid leaching process

Removal of silicate minerals from microcrystalline graphite ores is important to achieve high-purity graphite product. Alkali roasting pre-treatment and acid leaching process was used to prepare high-purity graphite from a fine microcrystalline graphite concentrate. The results showed that the alkali roasting pre-treatment and acid leaching process could enhance the fixed carbon of microcrystalline graphite to a higher level. Under the optimum conditions selected, a graphite product with fixed carbon content of 99.0% was obtained from microcrystalline graphite concentrate with carbon content of 90.2%. According to XRD and SEM-EDS analysis, impurities mainly composed of Fe, Si, and Al were decomposed to water soluble or acid soluble components during alkali-roasting pre-treatment and acid leaching process. The crystal structure and surface topography of microcrystalline graphite showed no change.     

How carbonation curing influences ca leaching of Portland cement paste: Mechanism and mathematical modeling

Carbonation curing provides a promising method for both CO₂ sequestration and strength improvement of cement-based materials. To date, there is little knowledge about the influence of carbonation curing on Ca leaching resistance of cement-based materials due to the occurrence of both physical and chemical transformation. It was the first time that Ca solid-liquid equilibrium curves were experimentally established for cement pastes with different carbonation degrees in this paper. Experimental results demonstrated that on the one hand, carbonation curing improves the leaching resistance of cement paste by sequestrating Ca in insoluble CaCO₃; on the other hand, potential negative effects may occur due to the accelerated decalcification and increased solubility of C–S–H after carbonation curing. Results of NMR showed that both carbonation curing and Ca leaching can increase the Si chain length and polymerization degree of C–S–H. Additionally, a modified mathematical model was established to simulate the leaching process of carbonation-cured cement paste and it was also verified by energy-dispersive spectroscopy (EDS) results. Therefore, the long-term leaching resistance of cement-based materials is possibly degraded by the carbonation curing treatment.     

Growth, composition, biological N2 fixation and nutrient uptake of a leguminous cover crop mixture and the effect of their removal on field nitrogen balances and nitrate leaching risk

Cover crops (CC) are an important source of nitrogen (N) in organic farming systems. Only few data are available about the effect of management activities (liquid slurry amendments, crop residue management) on growth, nutrient uptake and biological N₂ fixation (BNF) of a CC mixture. Furthermore, little information is available about the effect of CC harvesting on nutrient flows, nitrate leaching risk and soil mineral N supply of the succeeding main crop. The objectives of the presented field trials were (1) to measure the impact of organic manuring (straw residues and liquid slurry applications) on growth, composition, and BNF of a CC mixture with legumes and oil radish as components; (2) to determine the effect of CC species composition on nutrient content and uptake (N, P, K, Mg); and (3) to evaluate the effect of CC removal on field N balances and nitrate leaching risk. A CC mixture with legumes and non-legumes was able to compensate for many environmental and cultivation effects by influencing the competitive ability of the partners. For example, an increase of soil N supply due to additions of slurry or removal of cereal straw promoted growth of non-legumes at the expense of the legumes, resulting in N shortage at the end of the growing period, as shown by lower N contents and a wider C/N ratio of the non-legume partner. Low N availability at the beginning of the CC growth enhanced legume growth and/or reduced non-legume growth, resulting in a higher N supply in later periods of CC growth. A high legume percent composition within a CC mixture increases overall N content in the aboveground biomass and the N content of non-legumes within the mixture, and decreases the C/N ratio. Large amounts of nutrients were removed from the field by the harvesting of the CC aboveground biomass, significantly reducing the nitrate leaching risk. However, a reduction of the nitrate leaching risk was found only on fields where the green manure was incorporated in autumn.     

A novel method for enhancing on-stream stability of fluid catalytic cracking (FCC) gasoline hydro-upgrading catalyst: Post-treatment of HZSM-5 zeolite by combined steaming and citric acid leaching

This article describes a novel modification method consisting of steaming and subsequent citric acid leaching to finely tune acidity and pore structure of HZSM-5 zeolite and thereby to enhance the on-stream stability of the zeolite derived fluid catalytic cracking (FCC) gasoline hydro-upgrading catalyst. A series of dealuminated HZSM-5 zeolites and their derived catalysts were prepared and characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), ²⁷Al MAS NMR, nitrogen adsorption, temperature programmed desorption of ammonium (NH₃-TPD) and infrared (IR) spectroscopy of chemisorbed pyridine. The results showed that the citric acid leaching could preferentially remove the extra-framework Al (EFAl) species formed by steaming treatment and thus reopen the EFAl-blocked pore channels of the steamed zeolite. The steaming treatment at a suitable temperature and subsequent citric acid leaching not only decreased the strength of acid sites to a desirable degree but also increased the ratio of medium and strong Lewis acidity to medium and strong Brönsted acidity, both of which conferred the resulting catalyst with superior selectivity to aromatics, good hydroisomerization activity and gasoline research octane number (RON) preservability, as well as enhanced on-stream stability. The results fully demonstrated that the treatments by steaming and followed citric acid leaching can serve as an important method for adjusting the physicochemical properties of HZSM-5 zeolite.