Preparation of polyamidoamine dendrimer-functionalized chitosan beads for the removal of Ag(I), Cu(II), and Pb(II).

Chitosan bead grafted by third-generation dendrimers (CB-G3) with a diameter of 1.40 mm was synthesized to investigate their performance in recovering Ag(I), Cu(II), and Pb(II) ions in aqueous media. The prepared adsorbents were characterized by XRD, FT-IR, elemental analysis, TGA, and SEM, and the effects of pH, contact time, concentration, and temperature were examined. The results showed that the adsorbents were successfully fabricated. The optimum pH value was 5, and the increased generation number contributed to adsorption capacity improvement, indicating that electrostatic interactions between amine groups and metal ions are the governing mechanism of adsorption by the CB-G3. The kinetics, isotherms, and thermodynamics of Ag(I), Cu(II), and Pb(II) adsorption onto the CB-G3 were investigated. The adsorption processes can be described using pseudo-second-order kinetic and Langmuir models. The maximum monolayer adsorption capacities were 105.62, 88.82, and 97.87 mg·g-1 for Ag(I), Cu(II), and Pb(II) at 30 °C within 210 min, respectively. Electrostatic interactions and hydrogen bonds are the main mechanisms between metal ions and N atoms. Therefore, the CB-G3 is a promising candidate for Ag(I), Cu(II), and Pb(II) adsorption owing to its splendid ability in easy separation, good adsorptivity, and reusability for efficiently adsorbing Ag(I), Cu(II), and Pb(II) ions.

A comprehensive review of aluminium electrolysis and the waste generated by it.

Aluminium is produced by electrolysis using alumina (Al2O3) as raw material and cryolite (Na3AlF6) as electrolyte. In this Hall-Héroult process, the energy consumption is relatively large, and solid wastes such as spent anodes and spent pot liner, flue gas and waste heat are generated. Therefore, this article discusses from the perspective of high energy consumption and high pollution and summarizes the methods to reduce energy consumption and solve pollution problems. The functions of carbon anode, carbon cathode, refractory material and sidewall in aluminium electrolysis cells are discussed in detail. The process of aluminium electrolysis and the ways to improve the current efficiency of aluminium electrolysis cells and reduce their energy consumption are outlined. The causes and treatment methods of spent anodes, spent cathodes, spent refractories and spent spot liner are reviewed. The research progress of waste heat recovery and aluminium electrolysis flue gas purification are analysed. And the future research directions of aluminium electrolysis flue gas are provided.

Summary of research progress on separation and extraction of valuable metals from Bayer red mud.

Bayer red mud is a strong alkaline solid waste discharged during alumina production. Due to large emissions and strong alkalinity, red mud is now mostly dammed or buried, which not only occupies huge land but also contaminates the surrounding ecosystem, causing the risk of collapse and landslide. In addition to its overall utilization in building materials, agriculture, the environment, and the chemical industry, red mud also contains valuable metals such as sodium, aluminum, iron, titanium, and scandium and is considered to be an important secondary resource. In this paper, the physicochemical properties and hazards of red mud are first introduced, and then, the overall utilization of red mud is summarized. Then, the latest research progress on the separation and extraction of valuable metals from red mud is reviewed in detail and a new comprehensive utilization method is recommended and evaluated. This paper also provides suggestions for the future development direction of the comprehensive utilization technology of red mud.

Removal of Cr(VI) and Ag(I) by grafted magnetic zeolite/chitosan for water purification: Synthesis and adsorption mechanism.

In this paper, a novel grafted zeolite/Fe3O4/chitosan (ZMC-MAH-TEPA) adsorbent was greenly synthesized and evaluated for the removal of Cr(VI) and Ag(I) in single and bi-component solutions. The characterization data of XRF, XRD, FT-IR, VSM, TGA, BET and SEM showed the successful fabrication of the adsorbent with abundant -NH2 and -NH- as well as great recovery properties (11.70 emu/g). The effects of experimental parameters, including pH value, initial concentration, temperature, time, and coexisting ions on single and bi-component adsorption, were investigated. The results demonstrated that the adsorption capacities increased with the enhanced shaking time and concentration until equilibrium was reached. The optimum pH value was 3 for Cr(VI) adsorption and 5 for Ag(I) adsorption. The maximum adsorption capacities for Cr(VI) and Ag(I) ions, obtained by the Langmuir model, were 50.75 and 70.12 mg·g-1 in single metal solutions and 45.45 and 58.94 mg·g-1 in bi-component metal solutions (Cr(VI)/Ag(I) = 1:1), respectively. Additionally, the adsorption mechanism of Cr(VI) and Ag(I) was explained in terms of electrostatic interaction and hydrogen bonding between metal ions and -NH2 and -NH- in ZMC-MAH-TEPA. Taken together, this study provides a clean approach to synthesizing chitosan-based adsorbents for the efficient removal of Cr(VI) and Ag(I) ions.

Research on the Dealkalization Treatment of Bauxite Residue and Deep Extraction of Alumina.

Bauxite residue is the bulk solid waste generated by the alumina industry, and the environmental treatment of bauxite residue has always been a focus of attention. In this study, in the high calcium system, the bauxite residue was intensively digestion by the calcification-carbonation method, and the mole ratio of solution, the mass ratio of CaO/SiO2 of the digestion process were changed, so that the high-efficiency dealkalization of bauxite residue was realized and the aluminum oxide in bauxite residue was deeply extracted. The experimental results showed that the calcification process could achieve the recovery of 17.83% alumina at 260°C, reaction duration of 60 min, liquid-solid ratio = 5:1, the mass ratio of CaO/SiO2 = 3.5, and 200 g/L NaOH solution. The whole process can recover 49.61% of alumina from bauxite residue, and 94.4% of alkali in bauxite residue can be removed.

Research on the mechanism of sodium separation in bauxite residue synergy preparation of potassium-containing compound fertilizer raw materials by the hydrothermal method.

Bauxite residue poses an increasingly serious ecological safety problem in the alumina industry. A novel process for removing sodium in bauxite residue synergistic preparation of potassium-containing compound fertilizer raw materials was proposed to relieve pressure on the fertilizer industry. In this paper, synthetic sodalite and katoite were used to simulate the main mineral phases of bauxite residue to determine the suitable conditions for the method, and the transformation mechanism of the process was researched by analyzing the phase structure and microscopic morphology of the samples using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and specific surface area detection. The results show that the ideal reaction condition is 320 g/L K2O with solid reactants at 200 °C for 1 h. The separation rate of Na in the sodalite-katoite mixture reached 93.60%, with potassium aluminum silicate and katoite being the primary phases of the product, with a mesoporous structure and easy to be absorbed by crops. The bauxite residue transformation residue consisted of katoite and kaliophilite. With a total effective K2O, CaO, and SiO2 content of 38.22%, the Na2O content was 0.54%, meeting the requirements of compound fertilizer content on the market. The transformation mechanism is a dissolution-precipitation controlled sodium-potassium ion replacement reaction. This study provides theoretical guidance for the preparation of mineral fertilizer from bauxite residue and has practical production potential, opening up a new perspective for bauxite residue resource usage in the agricultural field.

Extraction and Utilization of Valuable Elements from Bauxite and Bauxite Residue: A Review.

Bauxite is the ideal raw material for the manufacturing of alumina. Aside from the primary constituents of aluminum and silicon, bauxite is frequently coupled with many valuable elements such as gallium (Ga), titanium (Ti), scandium (Sc), and lithium (Li). The bauxite residue and circulating spent liquor in alumina production typically include significant amounts of valuable elements, making them a potential source of polymetallic. The recovery of these essential components can greatly increase alumina manufacturing process efficiency while reducing industrial liability and environmental impact. This study gives a critical analysis of existing technology used to recover valuable elements from bauxite residue and circulating spent liquor to provide insight into the broader usage of bauxite residue as a resource rather than a waste. A comparison of existing process features demonstrates that an integrated process for valuable elements recovery and waste emission reduction is advantageous.

Calcification-Carbonation Method for Bayer Red Mud Treatment: Carbonation Performance of Hydrogarnets.

Hydrogarnets are vital intermediate products in the calcification- carbonation method, which is designed for Bayer red mud treatment. Their carbonation performance greatly depends on SiO2 substitution. In this study, different SiO2-substituted hydrogarnets were synthesized and characterized. Then, batch experiments were performed to evaluate the potential effects of important parameters such as CO2 pressure, and SiO2 substitution degree (x) on the carbonation process. The SiO2 substitution degrees of the hydrogarnets synthesized at 60, 120, 180, and 240°C were 0.27, 0.36, 0.70, and 0.73, respectively. As the SiO2 substitution degree increased, the hydrogarnet carbonation extents gradually declined. With an increase in CO2 pressure, the hydrogarnet carbonation percentages increased gradually and rose from 80.33% to 98.19% within 120 min. The phases detected in the carbonized products were strip-like aragonite as well as some calcite; the Al-rich and Si-rich phases in the carbonized products were amorphous.

Study on Iron Extraction from High Iron Bauxite Residue by Pyrite Reduction.

A new method of solid-phase reduction magnetic separation with pyrite as a reducing agent was proposed in order to realize resource utilization of high iron bauxite residue while reducing environmental harm. FeS2 powder and high iron bauxite residue powder were uniformly blended and roasted in a closed environment. A magnetic separator was utilized to separate the magnetic iron concentrate at 2400 GS, and the recovery rates were calculated. Experimental results show that the best iron recovery was 91.5% at 1:6 roasted bauxite: residue at 800℃ for 2 h. The recovery of Fe can be improved by reducing high iron bauxite residue with pyrite, and iron in both pyrite and high iron bauxite residue can be recovered simultaneously, alleviating the pressure of iron ore resources and improving its utilization value.

Experimental Research on Vortex Melting Reduction of High-Iron Red Mud (Bauxite Residue).

In this study, the advantages of the vortex melting reduction treatment of red mud were verified. Vortex melting reduction can improve the feeding rate, promote the reaction and the directional deposition of iron, which was conducive to the separation of slag and gold. The effects of different adding methods, stirring speed and reaction time on iron recovery were investigated by using red mud, aluminum leached slag and calcified slag as raw materials. According to the experiment, the best reaction conditions were that the raw material put into the furnace by rolling pellets, stirring speed 125 RPM, and reaction time 30 min. The results provided an experimental basis for the harmless and high-value utilization of high-iron red mud treated by vortex melting reduction.

Comprehensive Application Technology of Bauxite Residue Treatment in the Ecological Environment: A Review.

The emission of bauxite residue continues to grow with the increase of alumina production capacity, along with the large amounts of bauxite residue currently stored in stockpiles. The exposed problems of high yield, strong alkalinity, low comprehensive utilization rate, and threats to the ecological environment are becoming increasingly prominent. With the strict requirements of environmental protection, improving the comprehensive utilization rate of bauxite residue and bulk consumption of bauxite residue has become an urgent issue to be solved. A large number of researchers have conducted in-depth investigations into the application of bauxite residue over a wide range, and this paper summarizes its application in the environment in recent years, providing guidance for the high value and harmless application of bauxite residue, which can help reduce environmental pollution and human life and health hazards caused by bauxite residue.

Research on the oxidation characteristics of zinc sulfite in the zinc oxide desulfurization process.

Aiming at the pollution problem of low-content SO2 in non-ferrous metal production industry, the oxidation kinetics of zinc sulfite in the zinc oxide desulfurization process was studied. The concentration change of Zn2+, variation of pH, temperature and apparent activation energy in the oxidation process of two ZnSO3 samples were investigated systematically. The results indicate that the raw material with different crystal water has little effect on the oxidation kinetic of zinc sulfite. The reaction process comprises two stages: the dissolution process and the oxidation process. The zinc ion concentration is linearly rising with the action time during the oxidation process. The pH value rises quickly in the dissolution process and goes down slowly with reaction time in the oxidation process. The process is mainly controlled by a diffusion step and less effected by the temperature. The apparent activation energy Ea obtained for the two samples are 8.662 and 9.645 kJ/mol, respectively. Integrated with the kinetic model, the oxidation rate of zinc sulfite is controlled by the diffusion of HSO3- and O2 to the gas-liquid interface.

Green method to synthesize magnetic zeolite/chitosan composites and adsorption of hexavalent chromium from aqueous solutions.

This paper aims to synthesis a recyclable adsorbent from solid waste using a clean and environmentally friendly method to deal with Cr(VI) water pollution. Magnetic zeolite/chitosan composites (ZFA/MCS) were prepared by the neutralization method. The adsorption properties of ZFA/MCS, prepared by the neutralization method for Cr(VI) ions under different conditions especially cross-linking, were investigated in detail. The results showed that cross-linked ZFA/MCS generally showed higher adsorption capacity than uncross-linked ones. The uncross-linked ZFA/MCS and cross-linked ZFA/MCS showed a saturated adsorption capacity of 25.67 mg·g-1 and 28.47 mg·g-1 at pH = 3 and 30 °C, respectively. The experimental values were followed Langmuir adsorption equations and pseudo-second-order kinetic model, indicating that the adsorption was probably monolayer coverage and chemical adsorption, respectively. The effect of temperature proved that the adsorption was spontaneous and endothermic. Therefore, the adsorbent with excellent recyclability and adsorbability was successfully fabricated via a green synthetic strategy.

Simultaneous separation of Fe & Al and extraction of Fe from waste coal fly ash: Altering the charge sequence of ions by electrolysis.

A significant amount of coal fly ash is generated and this type of waste material causes severe environmental hazards. Metal (Al and Fe) extraction from coal fly ash is beneficial to the resource utilization of waste coal fly ash. However, the coexistence of Al and Fe in coal fly ash means that the separation of Al and Fe is required, which is a key and difficult step to prepare high value-added products from coal fly ash. This work presents a novel electrolysis method to alter the charge sequence of Al3+, Fe3+, and H2O, leading to a process different from their natural tendency for simultaneous separation of Fe3+ and Al3+, and extraction of Fe. The single iron removal efficiency was 43.48%, and the aluminum extraction efficiency was <0.30% under optimal conditions. The iron product had a purity of 98.3 wt% Fe, 0.45 wt% Al, and 0.18 wt% S. This process occurs without chemical additions and expensive membranes, avoiding impurity introduction, slag generation, and membrane limitations. Fe(s), H2(g), Al2(SO4)3(aq), and O2(g) are the main products during the electrolysis. Flake Fe is selectively produced instead of colloidal Fe(OH)3. Fe is a magnetic substance and is easier to remove from the solution by magnets than colloidal Fe(OH)3. H2 is a green fuel. Wastewater (Al2(SO4)3(aq)) can be directly used to further extract alumina. Therefore, this study provides an alternative method of zero pollution discharge for simultaneous separation of Fe3+ and Al3+, and extraction of Fe from coal fly ash leachate.

Clean production of porous-Al(OH)3 from fly ash.

Fly ash is one of the largest solid waste and causes serious environment problems. Extraction of Al(OH)3 from fly ash is beneficial to environment and economy. We developed a clean electrolysis method to generate hydroxyl groups in situ to extract Al(OH)3 from fly ash leachate without adding chemicals or using expensive membranes, avoiding the introduction of new impurities, secondary pollutants generation, and membrane limitations. Batch experiments yielded porous electrolytic products with BET surface areas from 11.7610 to 25.5267 m2/g, pore volumes from 0.1935 to 0.1643 cm3/g and pore sizes from 65.7960 to 25.7434 nm. The composition of the electrolytic products was 86.43 wt% Al(OH)3, 9.00 wt% SO3, 1.67 wt% Fe(OH)3, and 0.29 wt% Ca(OH)2. The current efficiency was 90.51 % under optimized conditions of c (Al3+) = 0.1 M, t =2 h, and J = 750 A/m2. Mean particle size was from 24.1-98.1 µm. Impurities mainly affected the composition of the electrolytic products. The OH- generated by H2O reduction reacted with Al3+, Fe3+, and Ca2+ to generate a hydroxide. Fe3+ preceded Ca2+ into the hydroxide. H2 released continuously from H2O reduction, resulting in a porous hydroxide. The wastewater was reused as a leaching reagent to promote zero-pollution discharge.

A perspective of stepwise utilization of hazardous zinc plant purification residue based on selective alkaline leaching of zinc.

A new route for selective recovery of zinc from hazardous zinc plant purification residue was proposed by alkaline leaching process. The thermodynamic analysis revealed that by controlling solution pH in the range from 14.30 to 16.78 at 25 °C, basic zinc sulfate can be converted to ZnO22- instead of Zn(OH)2, while Cd will enter into alkaline leaching residue as a hydroxide. It is feasible to leach selectively Zn and to separate it with Cd by alkaline leaching, and the experimental results confirm that. Under the conditions of NaOH concentration of 3 mol/L, L/S of 20 ml/g, temperature of 40 °C, and time of 50 min, LR of Zn reached 96.14% while them of Pb and Cd were only 0.66% and 2.83% respectively. ZnO with hexagonal wurtzite structure and Cd(OH)2 were the main phases of leaching residue. They crystallized and adhered to the surface of leaching residue particles, which result in the loose and random particle morphology. The findings confirm that alkaline leaching is efficient in separation of Zn and Cd in ZPPR. In addition, nano-ZnO with flowerlike was synthesized with the zinc-rich leaching solution by precipitation method and the its photocatalytic property was similar to that of nano-ZnO purchased.

Recovery of vanadium from calcification roasted-acid leaching tailing by enhanced acid leaching.

Vanadium contained tailing generated from the typical calcium roasting-acid leaching process is contaminant and waste of resource. Atmospheric and pressurized leaching were conducted and compared to recover the vanadium from the vanadium tailing and improve the tailing's environmental quality. Orthogonal experiments were designed and applied for the atmospheric leaching study. It is shown that the extraction efficiency of V changed from 29.6% to 43.5% while the extraction efficiency of Fe, Cr, Ti, Mg remained stable under 4% with variable atmospheric leaching conditions. In the pressurized leaching experiments, the effects of leaching temperature, H2SO4 concentration, liquid to solid ratio and leaching time on the extraction of V, Fe, and Ti were investigated. Under the optimum conditions (the temperature of 413.15 K, H2SO4 concentration of 300 g/L, liquid to solid ratio of 8:1 mL/g and the reaction time of 100 min), the extraction efficiencies of V, Fe, and Ti reached 91.7%, 60.1% and 46.5% respectively, a leach residue contains only 0.13% of stable vanadium was obtained.

Feasibility study on the use of thiosulfate to remediate mercury-contaminated soil.

The feasibility of using sodium thiosulfate to remediate the mercury-contaminated soil around a local chemical plant in northeastern China has been investigated. Effects of solid-to-reagent ratio and temperature on mercury extraction from soil samples with thiosulfate solutions were examined. BCR (European Community Bureau of Reference) analysis indicated that more than 90% of weak acid soluble and reducible mercury in the soil sample could be extracted by thiosulfate solution. Mercury extraction kinetics can be described by the two-step first-order reaction model in which the readily extractable fraction and the less extractable fraction of mercury were associated with their own rate constants. Mercury extraction with thiosulfate solutions could be slightly promoted when the contaminated soil was pre-oxidized with hydrogen peroxide. The results suggest that thiosulfate is a potentially effective complexing lixiviant in mercury-contaminated soil remediation.

Magnetic resonance imaging appearance of well-differentiated hepatocellular carcinoma.

OBJECTIVE: To investigate the magnetic resonance imaging (MRI) features of well-differentiated hepatocellular carcinoma (HCC). METHODS: We reviewed the MRI of 32 patients with 33 pathologically confirmed well-differentiated HCC. The MRI protocol included T2-weighted imaging with and without fat saturation, dual-phase T1-weighted imaging, and gadolinium-enhanced dynamic study. The signal intensity of each lesion was categorized as hyperintense, isointense, and hypointense with reference to the surrounding liver parenchyma. RESULTS: Thirty-one (93.9%) of 33 well-differentiated HCC were demonstrated on the MRI. The remaining 2 were isointense in all magnetic resonance sequences and, therefore, could not be identified. Most of them were hyperintense (n = 15 [45.4%]) or isointense (n = 16 [48.5%]) on T1-weighted imaging, and hyperintense (n = 12 [36.4%]) or isointense (n = 17 [51.5%]) on T2-weighted imaging. On the dynamic study, 17 lesions (51.5%) were enhanced. CONCLUSIONS: MRI may identify most well-differentiated HCC; however, the imaging appearance is diverse. Biopsy should be performed if magnetic resonance study is inconclusive.

Metastases from gastric carcinoma to colon in the form of multiple flat elevated lesions: a case report.

Gastric carcinoma is a common malignancy worldwide. Advanced stages of the disease may result in metastases to many other organs of the body. However, colonic metastases are rare. We report a case of gastric carcinoma with symptoms of abdominal fullness and weight loss. The serum carcinoembryonic antigen level was elevated. Esophagogastroduodenoscopy revealed giant folds occupying the whole gastric body and poor expansion of the stomach. Histologic examination of biopsy specimens from the giant fold demonstrated poorly differentiated adenocarcinoma with signet ring-cell differentiation. Total colonoscopy revealed five or six discrete flat elevated lesions in the distal transverse, descending, and sigmoid colons. These lesions were characterized by a clear margin of 3-5 mm in diameter and erosions on the tips. Polypectomy specimens demonstrated signet ring-cell carcinoma, which was histologically similar to the specimens taken from the gastric lesion. We conclude that this was a rare case in which gastric signet ring-cell carcinoma had metastasized to the colon in the form of flat elevated lesions, combined with rapid and wide lymphatic spread to the thorax and abdomen in a clinical course as short as 46 days.