Navneet Singh Randhawa

Anodic Dissolution Behaviour of Tungsten Carbide Scraps in Ammoniacal Media

In the present paper, potentiodynamic studies of WC scrap have been carried out as these studies give better idea about the anodic dissolution behaviour of the scrap material to recover the metal values. However, it has been seen that anodic passivation retards the dissolution of the scrap and adversely affects the recovery of metals. To minimize the passivity and to increase the anodic dissolution, some chemicals are often used as additives. Two different electrolytes namely hydrochloric acid and aqueous ammonia at varying concentrations had been employed for the above studies. The additives citric acid and oxalic acid were added to the acidic electrolyte whereas ammonium chloride, ammonium carbonate and ammonium sulphate were added in different concentration to the ammoniacal electrolyte. The studies revealed that 2% citric acid in 1N HCl was the optimum to achieve maximum anodic dissolution (current) of WC scrap. On the other hand, 5% NH4Cl was found suitable to obtain maximum anodic dissolution (current) in the ammoniacal (150 g/L) medium. The potentiodynamic studies were followed by the actual electrodissolution experiments in an electrolytic cell with the help of a rectifier. The W and Co recoveries were encouraging.

Direct electrolytic refining of end-of-life industrial copper waste scraps for production of high purity copper powder

The end-of-life electric cables from both domestic and industrial sources offer an attractive resource of copper metal. In addition, copper wastes generated during fabrication of copper components remains another valuable source of recyclable copper. This work reports a simple, cost-effective and eco-friendly direct electrolytic refining using waste electrical copper wire scrap and copper plate rejects for producing the value added high purity copper powder. Suitable anode support system was applied in which compressed wire scrap or copper plate rejects were held to make anode for electrolytic cell. Electrolysis parameters like current density, acid concentration and copper ion concentration were varied to arrive at optimum condition. Results showed the energy consumption of 1.44 kW h/kg at 89% current efficiency for producing the copper powder, that consisted of >80% of–325 mesh size particles, from waste copper wire anodes. However, slightly lower energy consumption of 1.32 kW h/kg at 91% current efficiency was observed during production of copper powder from copper fabrication rejects. The copper powder thus produced was characterised by chemical analysis, XRD and optical microscope to examine the purity and morphology etc. and found suitable for powder metallurgical applications. Present investigations have established the potential utilisation of copper waste wire scrap and copper plate rejects for the production of value added high purity copper powder.

Studies on dissolution kinetics of dolime in electrothermal magnesium slag

The electrothermal process of magnesium metal production is a promising route, where large sized internally heated reactor is used for magnesium production resulting in less energy and labour intensive and high space-time yield process. However, the dissolution behavior of dolime in the electrothermal slag has been found critical for the process optimization. In this paper, the dissolution kinetics of the dolime in the slag was discussed. Quaternary slag (CaO-Al2O3-SiO2-MgO) was prepared having basicity CaO/SiO2 ≥ 1.8 and Al2O3/SiO2 ≥ 0.26 for dolime dissolution studies by static hot dip method. Prior to the experiments, FactSage calculations were carried out varying temperatures and slag compositions. In the kinetic studies, dolime particles 10–15 mm size was added in slag melted at 1450, 1500 and 1550°C and samples were taken at various time intervals. The chemical analysis of slag sample was carried out to investigate the dissolution kinetics to establish the rate expression. The activation energy for the process was calculated for different models used in study and was found to be in the range of 130–270 kJ/mol. SEM analysis was done for surface analysis of reacted particles. This study would be helpful in optimizing the dolime charging rate during pilot scale trials for electrothermal magnesium production at CSIR-NML, Jamshedpur.

Thermodynamic consideration and phase evolution during oxidation of tungsten–copper electrical contactor scraps

Present studies account the feasibility studies on isothermal oxidation of W–Cu hard metal electrical contractor scraps for recycling by roasting-leaching method. This was investigated as one of main processes to produce friable oxidized product amenable to subsequent leaching process. Oxidation is facilitated using scrap turnings instead of solid W–Cu contactor rods. The alloy oxidizes to CuxO, WOx and CuWO4 upon heating in the temperature range 400–1000°C under oxygen flow. Apart from oxidized W and Cu phases, significant amount of Cu nuggets formed initially at 450°C that rose gravimetrically up to 750°C, and then disappeared at higher temperature. The maximum weight gain was about 22% compared to initial weight when oxidation was carried out at 750°C. Oxidation beyond the temperature of 750°C corresponded to significant loss of tungsten by evaporation of WO2 · (OH)2 gaseous product. Thermal oxidation of W–Cu metal electrical contractor tip scraps produced porous and friable oxidized product of W and Cu.