Synthesis of nickel oxalate particles in the confined internal droplets of W/O emulsions and in systems without space confinement

Nickel oxalate particles were synthesized in the confined internal aqueous phase droplets of water in oil (W/O) emulsions using the emulsion liquid membrane (ELM) system, with D2EHPA as the carrier and oxalic acid solution as the precipitating agent. The effect of parameters such as carrier concentration, mole ratio of nickel to oxalic acid and internal phase volume fraction of the emulsion on the rate of nickel uptake, characteristics of particles formed, their morphology and particle size distribution was investigated. Nickel oxalate particles were also synthesized in systems where confinement of space did not exist, such as the precipitation stripping (PS) technique and in homogenous solutions, under conditions similar as that in the ELM systems. Particles obtained in ELMs differed from particles obtained by other techniques in morphology and size. Evidence of cluster formation by diffusion limited aggregation and cluster–cluster aggregation was observed. Particle sizes of nickel oxalate synthesized in the confined space of water droplets in ELM systems were smaller by one order of magnitude in comparison with the other two methods. The mechanism of spheroid cluster formation by fast precipitation is elucidated. Controlled calcinations of the nickel oxalate particles yielded the commercially important nickel oxide particles that were granular in nature and porous in structure. The ELM and PS techniques provide technological options of recovering nickel from dilute waste streams and obtaining the commercially important oxide.