Recovery of Cobalt Ion into Polyethyleneglycol (PEG) Gel Phase as Thiocyanato Complex

Abstract

This study outlines the recovery of cobalt (Co) ion as a gel phase consists of PEG and Co-thiocyanato complex (Co(NCS)₄²⁻) from aqueous solution. Taking advantage of gel precipitation with composition written as (PEG)_nCo(NCS)₄K₂, a novel process for the efficient recovery of Co was proposed. Composition of gel phase and load capacity of Co ion in it was investigated by fundamental experiment. Gel precipitation from aqueous solution of nickel sulfate (NiSO₄), cobalt sulfate (CoSO₄) and potassium thiocyanate (KSCN) was observed by mixing it with polyethyleneglycol (PEG#4000, molar weight; 2,700∼3,500) aqueous solution. The results confirmed the large load capacity of Co (6.8 × 10⁻⁴ mol/1 g of gel phase) compared to the sorption to polyurethane foam reported in the past. Percentage of Co ion to the total amount of Ni and Co ions in gel phase were more than 99.6 at%, revealing excellent condensation efficiency for Co. Furthermore, Co ion was extracted and separated from SCN⁻ and PEG in gel phase, by utilizing solvent extraction. From the set of experimental results, feasibility of the proposed process was discussed.