Browsing by Author "Ho, E"
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- ItemBeneficial effect of iron oxide/hydroxide minerals on sulfuric acid baking and leaching of monazite(Elsevier B. V., 2022-05) Demol, J; Ho, E; Soldenhoff, KH; Karatchevtseva, I; Senanayake, GThe sulfuric acid bake/leach process is an established industrial process for the extraction of rare earths from hard-rock monazite ores/concentrates. The chemical reactions in the monazite acid bake can be strongly influenced by the gangue mineralogy of the ore/concentrate. In this work, the beneficial effect of three iron oxide/hydroxide minerals, namely hematite, goethite and magnetite, added to high grade monazite concentrate in the acid bake (temperature range of 200–800°) and leach process was investigated to understand the role of iron gangue. Baked solids and leach residues were characterised by elemental analyses, XRD, SEM-EDS and FT-IR. It was found that the addition of iron minerals to the monazite acid bake had a significant impact on bake chemistry, acting to significantly increase the leaching of both the rare earth elements and thorium, compared to monazite alone, mainly for temperatures above 300 °C. The increased dissolution of rare earth elements and thorium was attributed to the formation of an amorphous and insoluble iron sulfate-polyphosphate type phase in preference to insoluble rare earth and thorium containing polyphosphates identified during acid baking of monazite alone. After baking at 650 °C, the iron sulfate-polyphosphate type phase was altered to a more soluble form, leading to an increase in dissolution of iron, phosphorus and thorium. Acid baking at 800 °C led to the formation of FePO4, Fe2O3, CePO4 (monazite) and in some cases CeO2, causing a decrease in leaching of rare earths and thorium, and either an increase or a decrease in leaching of iron and phosphorus depending on the formation of FePO4 versus Fe2O3. Crown Copyright © 2022 Published by Elsevier B. V.
- ItemOxidants for uranium leaching(ALTA Metallurgical Services, 2007-05-24) Ho, E; Ring, RJMost uranium ores are leached with sulfuric acid under oxidising conditions. This paper reviews the oxidants that have been traditionally used in uranium leaching and discusses their merits in the context of overallow sheet considerations. Options for alternative oxidants are also discussed. In acid leaching, ferric ion (Fey) in solution oxidises insoluble uranium(IV) to soluble uranium(VI). Though ferric ion may be added directly, usually an oxidant is added to the circuit to convert ferrous ion to ferric ion in the liquor so that leaching can continue. The most common oxidants are pyrolusite and sodium chlorate. Pyrolusite is relatively cheap but introduces manganese ions into the liquor and consumes twice as much acid as sodium chlorate. Sodium chlorate is a slow reacting oxidant at low temperatures and acidities, and introduces chloride into the leach liquor. Caro ’s acid, HZSO5, is a non-polluting reagent that was used successfully at the Nabarlek uranium mine, and provided very good control of oxidising conditions. Other oxidants that are now being considered to overcome the disadvantages of pyrolusite and sodium chlorate are oxygen, hydrogen peroxide and SO/O2. Some performance data for these oxidants are presented. © The Authors
- ItemThe potential for uranium recovery at Nolans(ALTA Metallurgical Services, 2007-05-24) Soldenhoff, KH; Ho, E; Mackowski, SThe Nolans deposit, owned by Arafura Resources, Ltd, is located near Aileron in the Northern Territory of Australia. Initial rare earth mineralisation was detected in 1995, which was confirmed by further exploration work carried out from 1999 onwards. The rare earths are predominantly concentrated as rare earth phosphates, hosted by fluorapatite and cheralite. An essential part of the mineral chemistry of apatite (Ca5(PO4)3(F,OH)), is that the calcium phosphate structure does allow some substitution by rare earths and other ions, including uranium ions. Current mineral resources at Nolans, using a 1% REE cut-off grade, are 18.6 million tonnes at 3.1% rare earth oxide, 14.0% P205 and 0.021% U308. This resource can support a 10,000 tla REO operation for at least 20 years. The concentration of uranium in Nolans is higher than is typical of phosphate rock deposits worldwide. This requires appropriate management of the radioactivity during ore processing, but also provides an opportunity for recovery of uranium as a by-product. The recovery must be integrated into the rare earth process, which is the primary focus of the project. Furthermore, the separation of rare earths from the phosphate matrix and the recovery of phosphoric acid or other fertiliser products is also an important consideration. This paper discusses the various process options that are being considered for the development of a process for Nolans that integrates the recovery of phosphate values and uranium as by-products of rare earth processing. © The Authors