XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1239
MATERIALS AND METHODS
The ACL tails were rod-milled to ensure surface liberation
and homogeneity. The elemental composition and the min-
eralogy of the ground sample were determined using acid
digestion and X-ray diffraction (XRD), respectively. The
leaching reagents used in this study were 100% oxalic acid
(C2H2O4) and EDTA (C10H16N2O8).
A three-necked round-bottom flask was used for the
leaching experiments. A condenser and thermometer were
fitted on separate necks to maintain the temperature, while
an overhead stirrer with a collapsible impeller ensured con-
sistent mixing. The effects of temperature, reagent concen-
tration, and time on leaching efficiency were studied. To
ensure thorough mixing and prevent settling, the mixture
was stirred at 250 rpm, and a 1:10 solid-to-liquid ratio was
maintained. The second leaching stage involved treating the
oxalic acid leach residue with 0.2 mol/L EDTA under alka-
line conditions. The experiment was carried out in a conical
flask on a magnetic plate, and the stirrer was set to 350 rpm.
The concentration of the elements in the dissolved solution
was determined using an Inductively Coupled Plasma-
Optical Emission Spectroscopy (ICP-OES).
RESULTS &DISCUSSION
Sample Characterisation
The elemental composition of the slag was determined by
acid-digesting the sample and subjecting it to ICP analysis.
The obtained data is shown in Table 1. Iron Phosphates are
a major constituent of this feedstock. Rare earths are hosted
in both sulphates and undissolved phosphates. For brevity,
“total rare earth elements” will be referred to as “T-REE”
throughout this paper.
First-Stage Leaching
Behaviour of ACL Tailings in Oxalic Acid
The feed was subjected to 0.57 mol/L oxalic acid at different
temperature ranges: 25°, 45°, 65°, and 85°C for 24 hours.
The effectiveness of the proposed system was studied by
varying the time, temperature, and reagent concentration.
The results are presented in Figure 3.
Crushing/
Grinding
Acid Cracking
Water
Leaching
Flotation Ore Stockpile
Acid-Crack
Leach Residue
Flotation
Concentrate
Leach Liquor
Flotation
Tailings
Solvent
Extraction
Figure 2. Conventional REE extraction process (Gupta &Krishnamurthy, 2005)
Table 1. Elemental composition of ACL tailings
Element Al Ca Ce Dy Fe La Nd P Pr Th T-REE
%2.42 1.63 1.23 0.03 20.70 0.61 0.74 8.16 0.18 0.20 2.79
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XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1239
MATERIALS AND METHODS
The ACL tails were rod-milled to ensure surface liberation
and homogeneity. The elemental composition and the min-
eralogy of the ground sample were determined using acid
digestion and X-ray diffraction (XRD), respectively. The
leaching reagents used in this study were 100% oxalic acid
(C2H2O4) and EDTA (C10H16N2O8).
A three-necked round-bottom flask was used for the
leaching experiments. A condenser and thermometer were
fitted on separate necks to maintain the temperature, while
an overhead stirrer with a collapsible impeller ensured con-
sistent mixing. The effects of temperature, reagent concen-
tration, and time on leaching efficiency were studied. To
ensure thorough mixing and prevent settling, the mixture
was stirred at 250 rpm, and a 1:10 solid-to-liquid ratio was
maintained. The second leaching stage involved treating the
oxalic acid leach residue with 0.2 mol/L EDTA under alka-
line conditions. The experiment was carried out in a conical
flask on a magnetic plate, and the stirrer was set to 350 rpm.
The concentration of the elements in the dissolved solution
was determined using an Inductively Coupled Plasma-
Optical Emission Spectroscopy (ICP-OES).
RESULTS &DISCUSSION
Sample Characterisation
The elemental composition of the slag was determined by
acid-digesting the sample and subjecting it to ICP analysis.
The obtained data is shown in Table 1. Iron Phosphates are
a major constituent of this feedstock. Rare earths are hosted
in both sulphates and undissolved phosphates. For brevity,
“total rare earth elements” will be referred to as “T-REE”
throughout this paper.
First-Stage Leaching
Behaviour of ACL Tailings in Oxalic Acid
The feed was subjected to 0.57 mol/L oxalic acid at different
temperature ranges: 25°, 45°, 65°, and 85°C for 24 hours.
The effectiveness of the proposed system was studied by
varying the time, temperature, and reagent concentration.
The results are presented in Figure 3.
Crushing/
Grinding
Acid Cracking
Water
Leaching
Flotation Ore Stockpile
Acid-Crack
Leach Residue
Flotation
Concentrate
Leach Liquor
Flotation
Tailings
Solvent
Extraction
Figure 2. Conventional REE extraction process (Gupta &Krishnamurthy, 2005)
Table 1. Elemental composition of ACL tailings
Element Al Ca Ce Dy Fe La Nd P Pr Th T-REE
%2.42 1.63 1.23 0.03 20.70 0.61 0.74 8.16 0.18 0.20 2.79

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