John D. Donaldson

Heavy metals in the environment. Part II: a hydrochloric acid leaching process for the recovery of nickel value from a spent catalyst

Abstract A hydrochloric acid leaching process for the recovery of nickel, as nickel oxide, from low-grade spent catalyst analysing 17.7% Ni was studied. The effects of acid concentration, temperature, etc., on the extraction of nickel in chloride solution are first reported. Two different methods were examined for the separation of impurities from nickel chloride solution. In the first method, nickel was precipitated as solid nickel chloride by saturating the solution with hydrogen chloride gas. The effects of repeated leach/precipitation cycles were also investigated and it was found that the purity of the precipitated nickel chloride decreased as the number of cycles increased. Further purification was achieved by washing and anion exchange treatment. In the second method, nickel chloride solution was purified by removing impurities such as copper by cementation and iron and aluminium by oxidation/pH adjustment process. The preparation of nickel oxide from both methods was carried out by first precipitating nickel hydroxide, followed by calcination, to give an oxide with a purity suitable for the smelting process.

Separation of nickel from cobalt using electrodialysis in the presence of EDTA

Optimum conditions are determined for the removal of nickel from cobalt solutions by electrodialysis exploiting the greater stability of the EDTA complex with nickel. The Ni–(EDTA)2− complex and hydrated Co2+ ions are transferred from the feed solution to the electrodialysis anolyte and catholyte chambers, respectively. A three compartment cell is required to prevent the transfer of hydrated Ni2+ from the anolyte chamber as the EDTA present is destroyed at the anode. Complete removal of nickel from cobalt can be achieved but there is a compromise between cobalt purity and the percentage of cobalt transferred to the catholyte chamber for recovery.

Simultaneous recovery of heavy metals and degradation of organic species – copper and ethylenediaminetetra‐acetic acid (EDTA)

In mixed industrial effluent the presence of metal ions can retard the destruction of organic contaminants and the efficiency of recovery of metal is reduced by the presence of the organic species. Results are presented for a copper–ethylenediaminetetra-acetic acid (EDTA) system in which both effects occur. An electrochemical cell alone can be used to recover copper in pH range 1.5–4.5 but is not capable of achieving complete mineralisation of EDTA by anodic oxidation. A photolytic cell alone can achieve the destruction of EDTA at pH 3.5 but leaves copper in solution. A combined photolytic–electrochemical system using an activated carbon concentrator cathode achieves the rapid simultaneous destruction of EDTA and recovery of copper. n n n n© 2000 Society of Chemical Industry

Heavy metals in the environment. Part VI: Recovery of cobalt values from spent cobalt/manganese bromide oxidation catalysts

Abstract Cobalt is recovered from a series of spent cobalt/ manganese bromide oxidation catalysts containing 27–31% Co, 25–33% Mn, 0–14% Fe together with Cr, Cu and Ni. While ammoniacal leaching in the presence of reducing agents can be used to extract cobalt, the process has to be separately optimized for each sample. Leaching with 4 M HCl at 80°C for 4 hours, however, proved successful for all the catalysts. A method of successive neutralization is used for the separation of cobalt from the acid solutions. Addition of solid NaOH to pH 2 removes Fe and Cr as hydroxide, while addition of ammonia to pH 10 precipitates manganese oxide from an aerated solution leaving Co as a CoIII hexammine complex. Cobalt can be recovered from this solution by chemical or electrochemical processes. After crystallization the complex is converted to anhydrous cobalt chloride by heating it to 320°r to Co2O3 by roasting it in air at 500°C. Either of these materials may be readily converted into other cobalt chemicals. Alternatively, fluidized bed cell electrolysis of the CoIII. complex solution yields cobalt with purity > 99.5%.

Characterisation of the tin(II) hydroxide cation [Sn3(OH)4]2+, and the crystal structure of tritin(II) tetrahydroxide dinitrate

The crystal structure of Sn3(OH)4(NO3)2 has been determined using single-crystal X-ray diffraction and refined by full-matrix least-squares analysis to R1= 0.0323 and wR2= 0.1203. The complex crystallises in the monoclinic space group P21/n, with a= 7.729(1), b= 9.086(3), c= 14.159(3)A, β= 90.65(2)° and Z= 4. The tin(II) atoms are contained in discrete polynuclear [Sn3(OH)4]2+ cluster units in which each tin is bonded pyramidally to three short nearest-neighbour cluster hydroxide oxygen atoms. A distorted octahedron of oxygen atoms around the tin(II) atoms is completed by three longer contacts to nitrate oxygens in the directions in which the tin non-bonding electron pairs point. One of the OH groups in [Sn3(OH)4]2+ is unique in that it is bonded to all three cluster tin atoms. This cation is considered to be one of the main products of the hydrolysis of tin(II) in aqueous solution. Raman spectroscopic data for Sn3(OH)4(NO3)2 have also been obtained and the known Mossbauer data are discussed with reference to the structure.