Arsenic disposal is one of the most important environmental issues the mining and metallurgical industries are faced with. This problem has worsened in recent years because of the increasing arsenic content of the low-grade and complex ores currently processed by the mining industry and the introduction of stricter environmental regulations. / This Ph.D. thesis sought to develop a novel concept for arsenic fixation suitable for the long-term safe disposal of arsenic generated and disposed by the minerals industry. In particular this research project investigates the encapsulation of scorodite, a well characterized Fe(III)-As(V) compound having the following formula FeAsO4·2H2O, with phosphate coatings, materials potentially not prone to reductive decomposition. Reductive decomposition is known to be responsible for the release of arsenic into the environment form arsenate solids such as scorodite. / The subject matter of this thesis is the application of heterogeneous crystallisation techniques to produce stable phosphate coatings on scorodite particles. The experimental work reported in this thesis involved three different types of studies, namely (1) production of a number of synthetic minerals; (2) evaluation of their stability; and (3) encapsulation of scorodite with two of these synthetic minerals. The synthesis work involved the production of aluminium and calcium phosphates via homogeneous, heterogeneous and seeded crystallisation. The stability work involved the study of the dissolution of hydrated aluminium phosphate (AlPO4·1.5H2O), dicalcium phosphate dihydrate (CaHPO4·2H2O), and calcium-deficient hydroxyapatite (Ca10-x(HPO 4)x(PO4)6- x(OH)2-x, x <2). Finally, the encapsulation work involved the deposition of hydrated aluminium phosphate and calcium-deficient hydroxyapatite on scorodite particles and the evaluation of their stability in simulated oxic and anoxic environments. / The directed deposition of phosphate on scorodite particles was achieved via the control of supersaturation. For the directed deposition of aluminium phosphate, the supersaturation was controlled via pH adjustment. On the other hand, for the controlled deposition of calcium-deficient hydroxyapatite on scorodite particles supersaturation was controlled via regulated mixing of two Ca(II) and P(V) solutions at constant pH. Both encapsulation techniques appeared to enhance scorodite stability under simulated oxic and anoxic environments by reducing the arsenic release rate up to one order of magnitude.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.85929 |
| Date | January 2005 |
| Creators | Lagno, Felipe |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Mining, Metals and Materials Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002269606, proquestno: AAINR21666, Theses scanned by UMI/ProQuest. |
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