Removal Of Cobalt From Sulphate Solutions Using An Electrogenerative Process
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Date
2011-06
Authors
Tan, Wan Xin
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Publisher
Universiti Sains Malaysia
Abstract
An electrogenerative system is applied to removing cobalt from sulphate solutions. In this process, a chemical reaction takes place spontaneously in a divided cell where cobalt is reduced at the cathode and zinc is oxidised at the anode without an external supply of energy. In this work, two types of operating modes (batch reactor and batch-recycle reactor) were investigated.
The electrogenerative removal of cobalt is conducted in a batch reactor equipped with three-dimensional electrodes: 80 pores per inch (ppi) reticulated vitreous carbon (RVC) and porous graphite (PG-25) as cathode materials. Results obtained show that 80 ppi RVC serves as a more suitable cathode material than PG-25 in this system. At optimum conditions, more than 99% of cobalt was removed and recovered in its metallic state after 10 h of operation with an initial 200 mg L-1 Co(II) solution at pH 4.0 in 0.2 M Na2SO4 and 0.4 M H3BO3.
A flow-by reactor operated in a batch recirculation mode was also developed. RVC was used as the cathode material. Studies of Co(II) reduction on 100 ppi RVC were accomplished using 500 mg L-1 Co(II) concentration at pH 4.00 and with electrolyte flow rates of 50, 100, 150 and 200 mL min-1. It was shown that poor removal of < 75% cobalt was achieved at all flow rates after 8 h of operation. In another set of experiments, without pH adjustment throughout the experiments (initial pH = 5.44 ± 0.10), similar test solutions were used. It was noteworthy that a shorter time of 7 h was required to remove more than 99% of cobalt at all flow rates.
Therefore, further studies were done without pH adjustment. The use of 60 ppi RVC in the reactor resulted in the highest km value compared to other grades of RVC. km value was found to decrease with increasing cathode porosity under the experimental condition used.
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Keywords
An electrogenerative system is applied to removing , cobalt from sulphate solutions