The processing of laterite ores for the recovery of nickel and cobalt has increased as the
reserves of exploitable sulphide ores have become depleted. The pressure acid leach
process (PAL) has become the preferred option for the treatment of laterite ores.
Difficulties associated with the poor settling characteristics of the pulp in the counter
current decantation (CCD) circuit after pressure leaching has resulted in as much as
10% of the soluble nickel and cobalt reporting to the tailings. The objective of this
project is the development of an alternative processing step for the recovery of soluble
nickel and cobalt from the PAL tailings using resin-in-pulp (RIP) technology.
Commercially available chelating resins with the iminodiacetate functional group have
been studied for their suitability for the adsorption of nickel and other metal ions from
PAL tailings pulp. The Amberlite IRC 748 resin was found to be superior despite its
lower nominal loading capacity. The resin with the highest nominal capacity was
observed to adsorb less nickel as a result of the adsorption of greater amounts of the
impurity ions. The equilibrium loading for nickel on the preferred resin was found to be
similar from the ammonium and protonated form of the resin although the kinetics of
adsorption is greater when the resin is initially in the ammonium form.
A comprehensive study has been made of the equilibrium adsorption of several metal
ions on the resin as a function of the equilibrium pH of the solution. A relatively simple
model of the equilibrium adsorption which includes the effect of pH has been developed
ii
and the results compared with the experimental data obtained in the M2+/Na+/H+ system.
The model which requires two equilibrium constants has been found to fairly well
describe the experimental results.
A study of the kinetics of the loading of nickel and cobalt from both solutions and pulp
has shown that the rate can be described in terms of a first-order approach to
equilibrium. The kinetic and equilibrium parameters were used to simulate the
performance of a multi-stage counter current resin-in-pulp operation A semiquantitative
study of the elution of the adsorbed metal ions from the resin by dilute
sulphuric acid solutions was also undertaken.
The technical feasibility of the RIP process for the recovery of nickel and cobalt from
the PAL tailings has been successfully demonstrated in both laboratory and pilot-plant
studies using a five-stage adsorption process. Important parameters such as the
operating pH and the residence times of pulp and resin in each stage were identified
through the batch test work coupled to the simulation procedure.
The optimum pH for adsorption was found to be in the range 4 to 5 as this pH is high
enough to maximise the adsorption of nickel and cobalt while preventing precipitation
of nickel and cobalt as hydroxides from the pulp. A method for minimizing the
competition from more strongly loaded ions such as iron(II) and chromium(III) which
are present in the pulp was also developed in the initial laboratory phase of the project
and utilized during the pilot operation.
Problems associated with the preparation of the pulp preparation, elution of the loaded
resin and control of the adsorption train were resolved during several pilot plant runs on
site at a local PAL plant. These and other minor improvements and adjustments to the
operating procedure culminated in a successful continuous run for several days during
which the target recovery of 90% for nickel and 60% for cobalt was exceeded
throughout the run.
| Identifer | oai:union.ndltd.org:ADTP/221669 |
| Date | January 2005 |
| Creators | Zzainol@murdoch.edu.au, Zaimawati Zainol |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Zaimawati Zainol |
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