Heavy metals in the environment. Part I: Removal of cobalt from dilute effluent streams by fluidised bed electrolysis

The fluidised bed cell is an electrolytic reactor which is designed to provide higher ion-transfer conditions during electrolysis by breaking up the barrier layer at the cathode, thus enabling metals to be removed efficiently from dilute solutions. The effectiveness of the method as a means of removing metals from effluent to meet discharge consent levels is studied for the in-situ removal of cobalt from dilute solution. The effects of cathode density, pH, reaction time, buffer solution composition, buffer concentration and agitation on the removal of cobalt are reported and expressed in terms of the percentage removal of cobalt (α_Co), the efficiency for cobalt deposition (∞_Co), and the energy consumption (W_Co) for 1 kg of cobalt deposited. The results show that cobalt can, under optimised conditions, be removed from dilute solutions to a residual level of 0.2 ppm.     

Determination of the heat change in solvent extraction of metals. The extraction of zinc (II) from hydrochloric acid solutions by high molecular weight amines in various organic solvents

The heat change associated with the uptake of zinc (II) has been examined by using a twin type isoperibol calorimeter in the extraction of zinc (II) from hydrochloric acid solutions by trioctylamine hydrochloride (TOAHCl) and trioctylmethyl-ammonium chloride (TOMAC) in various organic solvents such as benzene, chlorobenzene, o-dichlorobenzene, toluene, m-xylene, nitrobenzene, carbon tetrachloride and 1, 2-dichloroethane. It was found that the dependence of apparent molar heat change (the value of the heat change detected with regard to the concentration of zinc (II) reacted) on the aqueous chloride concentration could be attributed to the change in the distribution of zinc (II) chloride species in the aqueous phase. Taking account of this fact, variable Y, which constitutes the sum of the change in enthalpies for the relevant steps in the extraction of zinc (II), except the transformation of ZnCl_j^(2-j)+ to ZnCl₄^2-, in the aqueous phase, is introduced. From the values of Y obtained, it is concluded that in the extraction by TOMAC, Y correlates with the solubility parameter of diluent, suggesting that the organic phases may be regarded as regular solutions, while in the extraction by TOAHCl, no clear-cut relation holds between Y and the physico-chemical constants of the diluent such as dipole moment, dielectric constant and solubility parameters.     

Current efficiency and kinetics of cobalt electrodeposition in acid chloride solutions. Part II: the influence of chloride and sulphate concentrations

The influence of cobalt chloride concentration, total chloride concentration and sulphate in the electrolyte on cobalt deposition were studied. The current efficiency increased and the overpotential for electrodeposition of cobalt decreased with increasing cobalt chloride concentration. Only minor changes were observed with addition of sodium chloride to the cobalt chloride solution. Sulphate electrolyte resulted in lower current efficiency and higher overpotential for electrodeposition when compared to a similar cobalt chloride electrolyte.     

Characterisation of cellulose treated by the steam explosion method. Part 2: Effect of treatment conditions on changes in morphology,degree of polymerisation,solubility in aqueous sodium hydroxide and supermolecular structure of soft wood pulp during steam explosion

An attempt was made to clarify the effect of steam explosion conditions on the changes in morphology, degree of polymerisation P_v, solubility towards aqueous alkali solution S_a, and supermolecular structure of a soft wood pulp and to elucidate the mechanism by which the steam explosion treatment makes natural cellulose completely soluble in aqueous alkali solution. For this purpose, scanning electron microscopic (SEM) observation and X-ray diffraction, solid-state cross-polarisation/magic-angle sample-spinning (CP/MAS) ¹³C nuclear magnetic resonance (NMR), S_a and P_v measurements were carried out on a series of soft wood pulps treated systematically by the steam explosion method. It was found that (1) the maximum S_a (c. 100%) was obtained when the soft wood pulp was treated under the conditions of steam pressure P = 2.9MPa and treatment time t = 30s, (2) the decrease in P_v of the pulp by the steam explosion resembled conventional acid hydrolysis of cellulose, (3) a higher water content in the sample to be treated gave a lower degree of decrease in P_v, (4) the repeated steam explosion method gave more fibrillated sample with higher S_a than the corresponding batch steam explosion, (5) the amorphous content of the samples as estimated by X-ray analysis decreased by the steam explosion, in spite of an increase in S_a, and (6) the structural parameters expressing the degree of breakdown in the intramolecular hydrogen bonds at the C₃ and C₆ positions, X_am(C₃) and X_am(C₆), of the samples as estimated by CP/MAS ¹³C NMR changed as functions of P and t, being almost parallel to S_a. This suggests that these parameters may be more closely correlated with S_a than with X_am(X) from X-ray analysis.     

Synthesis of molybdenum (IV) sulphide: Part II. Reaction of molybdenum (VI) oxide with (a) zinc sulphide and (b) cadmium sulphide in the presence of ammonium chloride

Reactions of molybdenum (VI) oxide with (a) zinc sulphide and (b) cadmium sulphide were studied in the temperature range 723–973 K. Small amounts of mixtures of molybdenum (IV) sulphide and molybdenum (IV) oxide, which are difficult to separate, were produced. When ammonium chloride was added to the reactants, 89.1% pure MoS₂ at 773 K and 96.17% pure MoS₂ at 798 K were produced in the case of zinc sulphide and cadmium sulphide respectively.