XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3429
stage of the work, the focus had been on probing their tech-
nical viability. So, optimisation of the technique was not
attempted.
LOW TEMPERATURE REMOVAL OF IRON
AS HEMATITE
In this part of the work, the precipitation of iron at
low temperature (100 °C) as hematite was explored in
an attempt to test whether the findings of previous stud-
ies (Riveros and Dutrizac 1996 and Dutrizac and Riveros
1999) wherein iron in a chloride media was precipitated as
hematite at low temperature (100 °C) was achieved.
The PLS was heated to 100 °C with continuous stir-
ring (200 rpm). When the target temperature was reached,
the stirring was increased to 400 rpm and hematite seed
(10 g) was added. Sodium hydroxide was then slowly added
to achieve the target pH (~4.0–4.5). When both the tar-
get temperature and pH have stabilised, oxygen gas was
injected (~3 L per minute) to oxidise any Fe(II) to Fe(III).
Subsamples of the solution for assay were withdrawn at an
hourly interval including. After four hours, the solution was
allowed to cool. The precipitates were observed to be well
formed and easily settled at the bottom of the reaction ves-
sel, when the agitation was stopped, and was filtered with
ease. This is contrast to the precipitate that is generated
when iron is removed from acidic leach solutions by partial
neutralisation. This approach is clearly an improvement.
The assay results, summarised Tables 3, show that
iron as well as aluminium and chromium were essentially
completely precipitated. So too were the barium, phospho-
rous and titanium. Substantial amounts of other transition
metals such cobalt, copper and nickel were also precipitated.
No manganese was precipitated. Its higher concentration in
the filtrate than the feed may be attributed to analytical error.
0
250
500
750
1,000
1,250
1,500
1,750
2,000
2,250
2,500
2,750
3,000
3,250
3,500
3,750
4,000
0
10
20
30
40
50
60
70
80
90
100
0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480
Time (minutes)
Mn SO2 Addition
Figure 2. Metal extraction and added SO
2 vs leaching time
Table 3. Change in the concentration of the metal ions after
iron removal
Sample ID Units Feed Filtrate
Al mg/L 1932 BDL
Ba mg/L 1 BDL
Ca mg/L 470 460
Co mg/L 129 103
Cr mg/L 16 BDL
Cu mg/L 74.6 NR
Fe mg/L 11290 3
K mg/L 3630 3100
Mg mg/L 524 582
Mn mg/L 115000 120200
Na mg/L 652 20350
Ni mg/L 67.5 43
P mg/L 110 BDL
Pb mg/L 17 NR
S mg/L 97220 89870
Ti mg/L 21 BDL
V mg/L 10.4 NR
Zn mg/L 121 34.4
BDL – Below detection level, shaded value henceforth
indicate BDL
NR – Not reported
SO2
Dosing
(g/kg)
Metal
Extraction
(%)
stage of the work, the focus had been on probing their tech-
nical viability. So, optimisation of the technique was not
attempted.
LOW TEMPERATURE REMOVAL OF IRON
AS HEMATITE
In this part of the work, the precipitation of iron at
low temperature (100 °C) as hematite was explored in
an attempt to test whether the findings of previous stud-
ies (Riveros and Dutrizac 1996 and Dutrizac and Riveros
1999) wherein iron in a chloride media was precipitated as
hematite at low temperature (100 °C) was achieved.
The PLS was heated to 100 °C with continuous stir-
ring (200 rpm). When the target temperature was reached,
the stirring was increased to 400 rpm and hematite seed
(10 g) was added. Sodium hydroxide was then slowly added
to achieve the target pH (~4.0–4.5). When both the tar-
get temperature and pH have stabilised, oxygen gas was
injected (~3 L per minute) to oxidise any Fe(II) to Fe(III).
Subsamples of the solution for assay were withdrawn at an
hourly interval including. After four hours, the solution was
allowed to cool. The precipitates were observed to be well
formed and easily settled at the bottom of the reaction ves-
sel, when the agitation was stopped, and was filtered with
ease. This is contrast to the precipitate that is generated
when iron is removed from acidic leach solutions by partial
neutralisation. This approach is clearly an improvement.
The assay results, summarised Tables 3, show that
iron as well as aluminium and chromium were essentially
completely precipitated. So too were the barium, phospho-
rous and titanium. Substantial amounts of other transition
metals such cobalt, copper and nickel were also precipitated.
No manganese was precipitated. Its higher concentration in
the filtrate than the feed may be attributed to analytical error.
0
250
500
750
1,000
1,250
1,500
1,750
2,000
2,250
2,500
2,750
3,000
3,250
3,500
3,750
4,000
0
10
20
30
40
50
60
70
80
90
100
0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480
Time (minutes)
Mn SO2 Addition
Figure 2. Metal extraction and added SO
2 vs leaching time
Table 3. Change in the concentration of the metal ions after
iron removal
Sample ID Units Feed Filtrate
Al mg/L 1932 BDL
Ba mg/L 1 BDL
Ca mg/L 470 460
Co mg/L 129 103
Cr mg/L 16 BDL
Cu mg/L 74.6 NR
Fe mg/L 11290 3
K mg/L 3630 3100
Mg mg/L 524 582
Mn mg/L 115000 120200
Na mg/L 652 20350
Ni mg/L 67.5 43
P mg/L 110 BDL
Pb mg/L 17 NR
S mg/L 97220 89870
Ti mg/L 21 BDL
V mg/L 10.4 NR
Zn mg/L 121 34.4
BDL – Below detection level, shaded value henceforth
indicate BDL
NR – Not reported
SO2
Dosing
(g/kg)
Metal
Extraction
(%)