Can ultimate recoverable resources (URR) be assessed? Does analyzing declining ore grades help?

Wellmer, F.-W., Scholz, R. W., & Bastian, D. (2023

Erschienen in Mineral Economics, April 2023, Ausgabe 36,

Inspired by a paper by Teseletso and Adachi (Miner Econ 8(10):21, 2021), the hypothesis regarding the declining grade of mined copper ore and its possible use as a guide to the future of ultimate recoverable resources (URRs) is tested. As a time axis, cumulative production is taken. Grades can be either grade of cumulative tonnage or annual production grade. Correlation can be linear (grade and tonnage) or semi-logarithmic (grade linear, tonnage logarithmic). We first show that the assumption that the highest correlation is the best guide to the future may be a fallacy. This is the linear correlation between grades of cumulative tonnage and cumulative tonnages since 1959, i.e., 85% of all copper mined historically with a near-perfect correlation approaching one (R2 = 0.97). This leads to implausibly low results of the URR, clearly demonstrating that this trend must shift in the future. Moreover, Teseletso and Adachi’s (Miner Econ 8(10):21, 2021) approach using a linear or semi-logarithmic correlation between annual grades with cumulative production leads to erroneous results. ...

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Closing the upcoming EU gypsum gap with phosphogypsum

Haneklaus, N.; Barbossa, S.; Basallote, M.D.; Bertau, M.; Bilal, E.; Chajduk, E.; Chernysh, Y.; Chubur, V.; Cruz, J.; Dziarczykowski, K.; Fröhlich, P.; Grosseau, P.; Mazouz, H.; Kiegiel, K.; Nieto, J.M.; Pavón, S.; Pessanha, S.; Pryzowicz, A.; Roubík, H.; Cánovas, C.R.; Schmidt, H.; Seeling, R.; Zakrzewska-Kołtuniewicz, G.

Published in Resources, Conservation and Recyling,  July 2022, volume 182, 106328

The EU Renewable Energy Directive with climate and energy goals does not leave room for coal-burning power plants that currently contribute approximately 17 million t of flue gas desulfurization (FGD) gypsum to EU manufacturers that require a total
of 57 million t of gypsum per year-  It is also unlikely that natural gypsum production in the EU can be significantly increased in the near-term. Unlike other critical raw materials (CRMs) such as rare earth elements (REEs) that constitute a relatively small volume and can be imported over long-distances, such practice is not economically feasible for this relatively inexpensive (per weight) bulk-commodity used in large quantities. Transport costs for natural gypsum easily surpass the product value, so that imports would measurably increase prices for construction in the EU and affect millions.

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Enhancing rare earth element transfer from phosphate rock to phosphoric acid using an inexpensive fly ash additive

Hakkar M.; Arhouni F.E.; Mahrou A.; Bilal E.; Bertau M.; Roy A.; Steiner G.; Haneklaus N.; Mazouz H.; Boukhair A.; Benjelloun M.

Published in ScienceDirect, October 2021, volume 172, 1071166

Adding active silica (SiO2) to reduce the free fluoride content is a known method to improve the filterability of phosphogypsum (PG) during wet phosphoric acid (WPA) processing of phosphate rock (PR). Besides, this process can also promote the transfer of valuable rare earth elements (REE) from the PR into the liquid phosphoric acid (PA) stream rather than into the solid PG matrix from which later economic recovery is more challenging. Khouribga PR, that shows total REE concentrations of 577 ppm (328 ppm heavy REE and 249 ppm light REE) of which yttrium (Y) with 240 ppm constitutes the major fraction, is processed at the Jorf Lasfar El-Jadida chemical complex in Morocco that is also home to the country’s largest coal power plant. Fly ash produced during thermal power production, 70% of which is stacked in the immediate vicinity, presently remains mostly unused and consists largely (48%) of silica. In this work the use of fly ash (34 kg per t PR) and pure silica (8.5 kg per t PR) on the transfer of REE from Khouribga PR into the PA and PG stream during dihydrate WPA production was examined. The inexpensive fly ash/silica additive increases the transfer of various REE to the PA stream. For Y an increase of 37% was measured that resulted in a concentration of 48 ppm in the PA stream prior to further concentration by evaporation.

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Uranium and other heavy metal sorption from Moroccan phosphoric acid with argan nutshell sawdust

Qamouche, K.; Chetaine, A.; El Yahayoui, A.; Moussaif, A.; Fröhlich, P.; Bertau, M.; Haneklaus, N.

Published in ScienceDirect, September 2021, volume 171

Argan nutshells, available in Morocco as a low-cost by-product from Argan oil production, were used to produce a sawdust biosorbent for the extraction of U and other heavy metals (Cd, As, Zn, Cu, Ni and Cr) from merchant-grade phosphoric acid (PA). Packed column (D = 20 mm, L = 250 mm, flowrate 1 mL/min) lab-scale experiments were carried out with three different solutions: (1) a synthetic heavy metals solution, (2) pure PA at different concentrations (0.85%, 8.5% and 85%) in water, and (3) merchant-grade PA from an industrial fertilizer plant in Morocco that was diluted with water to analyze different P2O5 contents (5%, 30% and 54%) and a U concentration of up to 157 ppm. The sawdust successfully adsorbed 99% of the U from (1) the synthetic solution and (2) the pure PA independent of the acid concentration. It further managed to adsorb more than half (54%) of U, 75% of Cd, 74% of As, 84% of Zn, 86% of Cu, 83% of Cr of the merchant-grade PA at 54% P2O5 content and a flow-rate of 1 mL/min. The sawdust was characterized by SEM and FTIR to understand the adsorption of metal ions. Column studies were carried out to know the breakthrough point. At breakthrough, the effluent volume was found to be 50 mL and the maximum adsorption capacity for U was found to be 0.93 mg/g. Heavy metal recovery using ANS does not seem to be promising as a result of the low (>10%) desorption rates if citric- or oxalic acid is used as was done in this study. Heavy metal extraction without direct recovery using ANS is promising and should further be investigated though.

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