aqueous alkaline medium
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Author(s):  
Ana Luiza Coelho Braga de Carvalho ◽  
Feliciana Ludovici ◽  
Daniel Goldmann ◽  
André Carlos Silva ◽  
Henrikki Liimatainen

AbstractA considerable amount of very fine particles can be found, e.g., stored in tailing ponds, and they can include valuable or hazardous minerals that have the potential to be recovered. Selective flocculation, i.e., the formation of larger aggregates from specific minerals, offers a promising approach to improve the recovery of ultrafine particles. This study focuses on the use of a new bio-based flocculation agent made of silylated cellulose nanofibers containing a thiol-functional moiety (SiCNF). Flocculation was performed in separated systems of ultrafine mineral dispersions of pyrite, chalcopyrite, and quartz in aqueous alkaline medium. The flocculation performance of SiCNF was addressed in terms of the turbidity reduction of mineral dispersions and the floc size, and the results were compared with the performance of a commercial anionic polyacrylamide. SiCNF exhibited a turbidity removal efficiency of approximately 90%–99% at a concentration of 4000–8000 ppm with chalcopyrite and pyrite, whereas the turbidity removal of quartz suspension was significantly lower (a maximum of approximately 30%). The sulfide particles formed flocs with a size of several hundreds of micrometers. The quartz in turn did not form any visible flocs, and the dispersion still had a milky appearance after dosing 12,000 ppm of the flocculant. These results open a promising path for the investigation of SiCNF as a selective flocculation agent for sulfide minerals. Graphical Abstract


2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Yuv Raj Sahu ◽  
Parashuram Mishra

Kinetics and mechanism of oxidation of carbenicillin by diperiodatocuprate [DPC-III] in aqueous alkaline medium were studied spectrophotometrically at 298 K and an ionic strength of 0.10 mol·dm−3. The reaction between DPC (III) and carbenicillin in the alkaline medium showed (CRBC : DPC-III) 1 : 4 stoichiometry. The reaction products were identified by the CHNS test, FT-IR, and LC-MS spectral reports. The reaction was of pseudo-first order with respect to DPC (III) and fractional order with respect to carbenicillin as well as alkali but retarding effect with respect to periodate. Monoperiodatocuprate (MPC-III) was found to be the main active species in the alkaline medium in the form of [Cu (H2IO6) (H2O)2]. Activation and thermodynamic parameters with respect to uncatalyzed rate constants (ku) and slow step rate constant (k) as well as equilibrium constants were determined. The plausible mechanism consistent with experimental results was proposed and discussed in detail.


Author(s):  
Thi Thyui Nguen ◽  
Nina Shaglaeva ◽  
Vladimir Novokshonov

As a result of improvement of the preparation procedure of tosyl-β-cyclodextrin in aqueous alkaline medium by the interaction of β-cyclodextrin with tosyl chloride (TosCl) at low temperatures, the yield of the target product was increased from 38% to 58%.


2020 ◽  
Vol 50 (4) ◽  
pp. 195-204
Author(s):  
Manjunath D. Meti ◽  
Sharanappa T. Nandibewoor ◽  
Shivamurti A. Chimatadar

2020 ◽  
Vol 44 (5-6) ◽  
pp. 295-300
Author(s):  
Priyamvada Sharma ◽  
Riya Sailani ◽  
Anita Meena ◽  
Chandra Lata Khandelwal

The kinetics and mechanism of the osmium(VIII)-catalysed oxidation of crotyl alcohol by hexacyanoferrate(III) in aqueous alkaline medium is studied. The role of the osmium(VIII) catalyst is delineated to account for the experimental observations. A plausible reaction mechanism is suggested. Activation parameters such as the energy and entropy of activation are evaluated by employing the Eyring equation and are found to be 36.833 kJ mol−1 and −141.518 J K−1 mol−1, respectively.


2020 ◽  
Vol 13 (1) ◽  
pp. 1641-1660
Author(s):  
S. Murcio-Hernández ◽  
A.V. Rueda-Solorio ◽  
J.A. Banda-Alemán ◽  
C. González-Nava ◽  
F.J. Rodríguez ◽  
...  

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