Application of membrane technology in a base metal refinery

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Date
2013Author
Nel, D.W.
Van der Gryp, P.
Neomagus, H.W.J.P.
Bessarabov, D.
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Nanofiltration (NF) has attracted much attention over the past few
years due to the reduced energy consumption compared to reverse
osmosis (RO) and better separation performance compared to
ultrafiltration (UF). Although research has been done in the area of
NF of nickel ions, sodium ions, and acid separation, not much
attention has been given to the separation of high nickel concentrations
from sulphuric acid streams. The use of NF for the
separation of nickel and acid from a spent nickel electrolyte is an
innovative process alternative for future industrial application
within a base metal refinery.
In this study, the separation performance of a composite
polyamide NF membrane on a spent nickel electrolyte was
investigated by varying the sodium sulphate concentration in the
feed (50–150 g/l ), the trans-membrane pressure (35-55 bar), and
cross-flow velocity (1.5-3.5 m/s), and measuring quantities such as
total permeate flux, acid rejection, nickel rejection, and sodium
rejection. The nickel and acid concentration in the feed were kept
constant with variations between 40-60 g/l and 25-40 g/l respectively,
while the temperature of the experiments was kept constant
at 50˚C.
The membrane was found to be very selective for nickel ions,
with the rejection of nickel ions varying between 54.4% and 98.2%.
The rejection of acid ions varied between -5.9% and 21.8%. The
rejection of sodium ions varied between 16.6% and 72.4% at a
cross-flow velocity of 2.5 m/s and sodium sulphate concentration of
50 g/l in the feed solution. An increase in trans-membrane pressure
increased the rejection of nickel, sodium, and acid ions, while an
increase in sodium sulphate concentration decreased the rejection of
nickel and acid ions.
The total permeate flux was found to increase with an increase
in trans-membrane pressure and decrease with an increase in
sodium sulphate concentration. The cross-flow velocity had an
insignificant effect on the total permeate flux and the rejection of
nickel, sodium and acid ions.