China 
Africa 
Explore chapters and articles related to this topic
Effect of consecutive deficiency of selenium and tungsten on production of acids and alcohols from CO
Published in Samayita Chakraborty, Biovalorisation of liquid and gaseous effluents of oil refinery and petrochemical industry, 2021
In the phase I of operation, in tungsten deficient operation, the bioreactor medium is continuously stirred. Thus the biomass should be homogenously distributed and that biomass adhered to the reactor was used as the inoculum for the next assay. Phase II of operation was initiated with complete withdrawal of the bioreactor medium, while fresh medium was added to the bioreactor. It contained tungsten in the form of sodium tungstate at a concentration of 2 mg/L as trace element, but no selenium (in the form of selenate). Otherwise, the same operating procedure was followed as in phase I. According to the production of acids and alcohols, the acetogenic phase lasted for 6 days and the solventogenic phase (pH of 4.9) lasted from days 7-21. Two samples (1 mL each) were collected after 24 hours and the mean value of the biomass and metabolites concentrations were recorded.
Producing Fuels and Fine Chemicals from Biomass using Nanomagnetic Materials
Published in Vanesa Calvino-Casilda, Antonio José López-Peinado, Rosa María Martín-Aranda, Elena Pérez-Mayoral, Nanocatalysis, 2019
Aiming to a similar objective of a one pot production of HMF derivatives directly from fructose, but using only one catalyst, a magnetic bi-functional WO3HO-VO(salten)-SiO2@Fe3O4 nanocatalyst has been recently prepared (Mittal et al. 2016). The catalyst was used to synthesize 2,5-diformylfuran (2,5-DFF) from fructose. The chlorosilylated SiO2@Fe3O4 (Cl-SiO2@Fe3O4) nanoparticles served as the nanomagnetic platform for the two functionalities. Tungstic acid was generated via the protonation of sodium tungstate. Oxovanadium was complexed with a salten ligand. Under the optimal one-pot system, tungstic acid-mediated fructose dehydration afforded 82% conversion into 5-hydroxymethylfurfural (5-HMF) in 1 hr. The nanocatalyst was retrieved magnetically and re-used up to five times with marginal losses in the activity.
Flame Retardance of Fabrics
Published in Menachem Lewin, Stephen B. Sello, Handbook of Fiber Science and Technology: Chemical Processing of Fibers and Fabrics, 2018
It appears that the negatively charged groups, such as carboxyl and sulfhydryl, do not participate in the reaction with the negatively charged complex ions. Amino and imidazol groups, however, have a strong affinity to the metal complexes. Sulfated wool shows a zero level uptake since the –OSO3 residues electrostatically repel the negatively charged fluorozirconate anions. A similar phenomenon would also be expected in the case of shrinkproofed or oxidized wool, when a part of the cystine linkages are oxidized to cysteic residues [337–339]. The ZrF62- ion is probably situated in the cuticle and outer cortex of the fibers [331]. The maximum amount sorbed on the wool is 1.8% Zr as fluorozirconate. In the presence of sodium tungstate and citric acid, 98% exhaustion of the bath is obtained. The addition of Na2WO4 also increases the wash fastness of the treated fabrics to about 50 washes at temperatures up to 40°C. The treated fabrics, however, do not pass the DOC FF-3-71 [331] which requires laundering at 60°C. The K2ZrF6 in the wool appears to hydrolyze during alkaline launderings to ZrO2, which is trapped within the fibers and appears to be the virtual active flame retardant. It appears that the Zr and Ti complexes operate in the condensed phase as evidenced by the results in Fig. 1.15. It is not surprising that these complexes reduce even further the smoke obscuration upon combustion of treated wools, in view of the known effect on smoke of many other metallic compounds (see Sec. 3.9).
Bi2WO6 nanoflakes incorporated carbon nanofibers to control biological and chemical pollutants: bifunctional application
Published in Chemical Engineering Communications, 2022
M. Shamshi Hassan, Vineet Tirth, Ali Q. Alorabi, Firoz Khan, Ali Algahtani, Touseef Amna
The sodium tungstate solution was prepared by dissolving Na2WO4·2H2O (1.649 g, Sigma-Aldrich, >99.0%) in 50 ml water. In a separate beaker, Bi(NO3)3·5H2O (2.425 g, Sigma-Aldrich, >98.0%) was dissolved in solution of acetone and water (1:4, v/v). Afterwards, this mixture was slowly added to sodium tungstate solution, properly mixed, and then ammonia solution (25%, Samchun Chemicals) was added drop wise till pH of the solution reached 9. The final solution was shifted to autoclave reactor and heated at 180 °C for 48 h. The sample was filtered and washed with distilled water and ethanol, dried under vacuum at 80 °C for 12 h. For the synthesis of CNFs-Bi2WO6 nanocomposite, same method was applied with addition of 100 mg of CNFs (Carbon Nano-Material Technology Co. Ltd., South Korea) in solution.
Recovery of tungsten and cobalt from cemented tungsten carbide wastes using carbonate roasting and water leaching
Published in Journal of the Air & Waste Management Association, 2021
So Yeong Byun, Jong Sun Park, Jong Hyeok Kang, Sangyun Seo, Tam Tran, Myong Jun Kim
The novel technique for processing and recovering W and Co studied and reported herewith relies on the formation of water-soluble sodium tungstate (Na2WO4) by roasting the WC-Co scraps in Na2CO3. The advantage offered by this technique is that CO2 is liberated and not contaminating the residues. Water was used to dissolve Na2WO4 whereas Co oxide containing impurities remains in the leach residue that can be further processed to produce Co final products. Results of thermodynamic modeling of different processes used and of the experimental study to determine the optimized conditions for roasting and leaching are reported in this paper.
Reclamation of tungsten from spent HDS catalyst: a detailed study
Published in Indian Chemical Engineer, 2022
Surjeet Mahalik, A. R. Sheik, Barsha Dash, C. K. Sarangi, K. Sanjay
The HDS spent catalyst was devolatilized at 650°C to remove all oils and organics. The catalyst having tungsten aluminium and nickel in their sulfide form got converted to the corresponding oxide form. The oxidised catalyst was leached with NaOH to get tungsten in the form of water soluble sodium tungstate which is again converted to tungstic acid by acidification. Tungstic acid after roasting forms tungsten trioxide which after H2 reduction gets converted to tungsten metal with 99.97% purity. Nickel was also recovered as Nickel Hydroxide as a by-product. This detailed study is quite useful to extract tungsten from tungsten bearing secondaries.