1648 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
is to date no comprehensive study of how phyllosilicate
crystal chemistry affects dissolution behavior in leaching.
Applying crystal chemistry plus nanoscale examination of
samples before and after leaching would help to quantify
what fractions of the different layers in the phyllosilicate
structure remain intact under what conditions.
There are also a number of unanswered questions
about what happens to various mineral components dur-
ing leaching. For instance, there are no published data on
the compositions of silica gels and little in the literature
about whether they incorporate elements other than silica.
Analyses from industry suggest that silica gels developed in
leaching are a multi-component mix (Barton, unpublished
data), but whether the non-silica fractions come from
incorporating undissolved mineral components, complexes
adsorbed from solution, or both is unknown. Similarly,
Terry’s (1983a) suggestion that phyllosilicates with a T-O
structure dissolve faster and more completely than their
T-O-T equivalents has not been seriously tested.
Lastly, how all this geometallurgical detail about phyl-
losilicates relates to production-scale phenomena is an open
question. The reaction of phyllosilicates in relatively pure
acid solutions in the lab may be relatively simple, but the
raffinates used in practical leaching are far from pure. The
dissolved ions they contain at high concentrations, notably
Mg, Fe, and Al, probably inhibit dissolution of the same
ions from minerals in the ore. This may slow some of the
phyllosilicate decrepitation observed in laboratory stud-
ies, and complicates the incongruent dissolution of gangue
minerals including phyllosilicates. As an example, bond
strength may predict that Mg would dissolve to a greater
extent than Al from a phyllosilicate containing both but
if the solution is Mg-saturated and Al-undersaturated the
opposite may be the case. In conclusion, crystal chemistry
and similar mechanistic factors in dissolution modeling are
certainly important on the laboratory scale, but translat-
ing their influence into production-scale effects is at present
difficult.
ACKNOWLEDGMENTS
The material briefly presented here has grown from several
more detailed previous studies with multiple collaborators.
Particular thanks are due to Pierre-Marie Zanetta, Nicholas
Tillotson, Max Drexler, and Molly Radwany. Rodney
Saulters (Freeport-McMoRan) and Jodie Robertson pro-
vided helpful data and discussions of silica gel formation.
REFERENCES
Aagaard, P., and Helgeson, H.C., 1982. Thermodynamic
and kinetic constraints on reaction rates among min-
erals and aqueous solutions. I. Theoretical consider-
ations. American Journal of Science 282: 237–285.
Barton, I., Drexler, M., Radwany, M., and Zanetta,
P.M., 2023. Leaching metals from phyllosilicate ores.
Proceedings of the 9th International Symposium on
Hydrometallurgy, paper #3225.
Baum, W., 1999. The use of a mineralogical data base for
production forecasting and troubleshooting in cop-
per leach operations. Proceedings of the Copper 99 /
Cobre 99 International Conference, 393–408.
Chetty, D., 2018. Acid-gangue interactions in heap leach
operations: a review of the role of mineralogy for pre-
dicting ore behaviour. Minerals 8.47: 11 p.
Drexler, M., Barton, I.F., and Zanetta, P.M., 2023.
Vanadium in phyllosilicate ores: Occurrence, crystal
chemistry, and leaching behavior. Minerals Engineering
201: 108205.
Graefe, M., Klauber, C., McFarlane, A.J., and Robinson,
D.J., eds., 2017. Clays in the Minerals Processing
Value Chain. Cambridge University Press: 450 p.
Li, J., McFarlane, A., Klauber, C., and Smith, P., 2017.
Chapter 3: Leaching and solution chemistry. In: Graefe,
M., Klauber, C., McFarlane, A.J., and Robinson, D.J.,
eds., Clays in the Minerals Processing Value Chain:
111–141.
Lu, J., Dreisinger, D., and West-Sells, P., 2017. Acid curing
and agglomeration for heap leaching. Hydrometallurgy
167: 30–35.
Matthew, I.G., and Elsner, D., 1977. The hydrometal-
lurgical treatment of zinc silicate ores. Metallurgical
Transactions B 8B: 73–83.
McDonald, R.G., and Whittington, B.I., 2008.
Atmospheric acid leaching of nickel laterites review.
Part I. Sulphuric acid technologies. Hydrometallurgy
91: 35–55.
Mulders, J., and Oelkers, E.H., 2020. An experimental
study of sepiolite dissolution rates and mechanisms
at 25 °C. Geochimica et Cosmochimica Acta 270:
296–312.
Ndlovu, B., Forbes, E., Farrokhpay, S., Becker, M.,
Bradshaw, D., and Deglon, D., 2014. A preliminary
rheological classification of phyllosilicate group miner-
als. Minerals Engineering 55: 190–200.
Oelkers, E.H., Schott, J., and Devidal, J.L., 1994. The effect
of aluminum, pH, and chemical affinity on the rates of
aluminosilicate dissolution reactions. Geochimica et
Cosmochimica Acta 58.9: 2011–2024.
is to date no comprehensive study of how phyllosilicate
crystal chemistry affects dissolution behavior in leaching.
Applying crystal chemistry plus nanoscale examination of
samples before and after leaching would help to quantify
what fractions of the different layers in the phyllosilicate
structure remain intact under what conditions.
There are also a number of unanswered questions
about what happens to various mineral components dur-
ing leaching. For instance, there are no published data on
the compositions of silica gels and little in the literature
about whether they incorporate elements other than silica.
Analyses from industry suggest that silica gels developed in
leaching are a multi-component mix (Barton, unpublished
data), but whether the non-silica fractions come from
incorporating undissolved mineral components, complexes
adsorbed from solution, or both is unknown. Similarly,
Terry’s (1983a) suggestion that phyllosilicates with a T-O
structure dissolve faster and more completely than their
T-O-T equivalents has not been seriously tested.
Lastly, how all this geometallurgical detail about phyl-
losilicates relates to production-scale phenomena is an open
question. The reaction of phyllosilicates in relatively pure
acid solutions in the lab may be relatively simple, but the
raffinates used in practical leaching are far from pure. The
dissolved ions they contain at high concentrations, notably
Mg, Fe, and Al, probably inhibit dissolution of the same
ions from minerals in the ore. This may slow some of the
phyllosilicate decrepitation observed in laboratory stud-
ies, and complicates the incongruent dissolution of gangue
minerals including phyllosilicates. As an example, bond
strength may predict that Mg would dissolve to a greater
extent than Al from a phyllosilicate containing both but
if the solution is Mg-saturated and Al-undersaturated the
opposite may be the case. In conclusion, crystal chemistry
and similar mechanistic factors in dissolution modeling are
certainly important on the laboratory scale, but translat-
ing their influence into production-scale effects is at present
difficult.
ACKNOWLEDGMENTS
The material briefly presented here has grown from several
more detailed previous studies with multiple collaborators.
Particular thanks are due to Pierre-Marie Zanetta, Nicholas
Tillotson, Max Drexler, and Molly Radwany. Rodney
Saulters (Freeport-McMoRan) and Jodie Robertson pro-
vided helpful data and discussions of silica gel formation.
REFERENCES
Aagaard, P., and Helgeson, H.C., 1982. Thermodynamic
and kinetic constraints on reaction rates among min-
erals and aqueous solutions. I. Theoretical consider-
ations. American Journal of Science 282: 237–285.
Barton, I., Drexler, M., Radwany, M., and Zanetta,
P.M., 2023. Leaching metals from phyllosilicate ores.
Proceedings of the 9th International Symposium on
Hydrometallurgy, paper #3225.
Baum, W., 1999. The use of a mineralogical data base for
production forecasting and troubleshooting in cop-
per leach operations. Proceedings of the Copper 99 /
Cobre 99 International Conference, 393–408.
Chetty, D., 2018. Acid-gangue interactions in heap leach
operations: a review of the role of mineralogy for pre-
dicting ore behaviour. Minerals 8.47: 11 p.
Drexler, M., Barton, I.F., and Zanetta, P.M., 2023.
Vanadium in phyllosilicate ores: Occurrence, crystal
chemistry, and leaching behavior. Minerals Engineering
201: 108205.
Graefe, M., Klauber, C., McFarlane, A.J., and Robinson,
D.J., eds., 2017. Clays in the Minerals Processing
Value Chain. Cambridge University Press: 450 p.
Li, J., McFarlane, A., Klauber, C., and Smith, P., 2017.
Chapter 3: Leaching and solution chemistry. In: Graefe,
M., Klauber, C., McFarlane, A.J., and Robinson, D.J.,
eds., Clays in the Minerals Processing Value Chain:
111–141.
Lu, J., Dreisinger, D., and West-Sells, P., 2017. Acid curing
and agglomeration for heap leaching. Hydrometallurgy
167: 30–35.
Matthew, I.G., and Elsner, D., 1977. The hydrometal-
lurgical treatment of zinc silicate ores. Metallurgical
Transactions B 8B: 73–83.
McDonald, R.G., and Whittington, B.I., 2008.
Atmospheric acid leaching of nickel laterites review.
Part I. Sulphuric acid technologies. Hydrometallurgy
91: 35–55.
Mulders, J., and Oelkers, E.H., 2020. An experimental
study of sepiolite dissolution rates and mechanisms
at 25 °C. Geochimica et Cosmochimica Acta 270:
296–312.
Ndlovu, B., Forbes, E., Farrokhpay, S., Becker, M.,
Bradshaw, D., and Deglon, D., 2014. A preliminary
rheological classification of phyllosilicate group miner-
als. Minerals Engineering 55: 190–200.
Oelkers, E.H., Schott, J., and Devidal, J.L., 1994. The effect
of aluminum, pH, and chemical affinity on the rates of
aluminosilicate dissolution reactions. Geochimica et
Cosmochimica Acta 58.9: 2011–2024.