Minerals2015, 5(1), 86-103; doi:10.3390/min5010086 - published 3 February 2015 Show/Hide Abstract
Abstract: The failure of a tailing dam occurs due to damage to the particles’ micro-structure. Understanding the deformation characteristics of the particle’ micro-structure is important for understanding the mechanics of instability in tailing dams. In our study, a series of experiments was conducted using a testing apparatus for micro-mechanics and the deformation of tailings from the Huangcaoping tailing pond, Sichuan Province, China to investigate the loading capacity, micro-structure and deformation features of tailing particles. The latter two were analyzed quantitatively using concepts from fractal geometry. The results demonstrate that: (1) the structural loading capacity of tailings increases first and then decreases slightly with increasing particle size; (2) the particle micro-structure of the four tailing samples from the Huangcaoping tailing pond is described in terms of the fractal dimension based on the perimeter and area (D-value), which is between 1.288 and 1.533; (3) as the axial stress increases, the D-value gradually decreases along a wavy line with a decreasing rate of change; (4) under the same axial strain, the D-value first decreases and later increases slightly as the particle size increases; and (5) the number of fractured particles increases with the particle size.
Minerals2015, 5(1), 82-85; doi:10.3390/min5010082 - published 19 January 2015 Show/Hide Abstract
Abstract: Mining is a vital part of the Global economy, but the extraction of metals, metalloids, and other mineral products generates vast quantities of liquid and solid waste. Currently the volume is estimated at several thousand million tons per annum, but is increasing exponentially as demand and exploitation of lower-grade deposits increases. The high concentrations of potentially toxic elements in these wastes can pose risks to ecosystems and humans, but these risks can be mitigated by implementing appropriate management or remediation schemes. Although there are a large number of such schemes available, there is still a need to research the processes, products, and effectiveness of implementation, as well as the nature of the mine wastes themselves. This Special Issue is aimed at bringing together studies in the areas of mine waste characterization, management, and remediation, to review the current state of knowledge and to develop improvements in current schemes. Fourteen manuscripts are published for this Special Issue, and these are summarized below.[...]
Minerals2015, 5(1), 61-79; doi:10.3390/min5010061 - published 30 December 2014 Show/Hide Abstract
Abstract: Mogok gem corundum samples from twelve localities were analyzed for trace element signatures (LA-ICP-MS method) and oxygen isotope values (δ18O, by laser fluorination). The study augmented earlier findings on Mogok gem suites that suggested the Mogok tract forms a high vanadium gem corundum area and also identified rare alluvial ruby and sapphire grains characterised by unusually high silicon, calcium and gallium, presence of noticeable boron, tin and niobium and very low iron, titanium and magnesium contents. Oxygen isotope values (δ18O) for the ruby and high Si-Ca-Ga corundum (20‰–25‰) and for sapphire (10‰–20‰) indicate typical crustal values, with values >20‰ being typical of carbonate genesis. The high Si-Ca-Ga ruby has high chromium (up to 3.2 wt % Cr) and gallium (up to 0. 08 wt % Ga) compared to most Mogok ruby (<2 wt % Cr; <0.02 wt % Ga). In trace element ratio plots the Si-Ca-Ga-rich corundum falls into separate fields from the typical Mogok metamorphic fields. The high Ga/Mg ratios (46–521) lie well within the magmatic range (>6), and with other features suggest a potential skarn-like, carbonate-related genesis with a high degree of magmatic fluid input The overall trace element results widen the range of different signatures identified within Mogok gem corundum suites and indicate complex genesis. The expanded geochemical platform, related to a variety of metamorphic, metasomatic and magmatic sources, now provides a wider base for geographic typing of Mogok gem corundum suites. It allows more detailed comparisons with suites from other deposits and will assist identification of Mogok gem corundum sources used in jewelry.
Minerals2015, 5(1), 1-60; doi:10.3390/min5010001 - published 24 December 2014 Show/Hide Abstract
Abstract: This review has as its underlying premise the need to become proficient in delivering a suite of element or metal products from polymetallic ores to avoid the predicted exhaustion of key metals in demand in technological societies. Many technologies, proven or still to be developed, will assist in meeting the demands of the next generation for trace and rare metals, potentially including the broader application of biohydrometallurgy for the extraction of multiple metals from low-grade and complex ores. Developed biotechnologies that could be applied are briefly reviewed and some of the difficulties to be overcome highlighted. Examples of the bioleaching of polymetallic mineral resources using different combinations of those technologies are described for polymetallic sulfide concentrates, low-grade sulfide and oxidised ores. Three areas for further research are: (i) the development of sophisticated continuous vat bioreactors with additional controls; (ii) in situ and in stope bioleaching and the need to solve problems associated with microbial activity in that scenario; and (iii) the exploitation of sulfur-oxidising microorganisms that, under specific anaerobic leaching conditions, reduce and solubilise refractory iron(III) or manganese(IV) compounds containing multiple elements. Finally, with the successful applications of stirred tank bioleaching to a polymetallic tailings dump and heap bioleaching to a polymetallic black schist ore, there is no reason why those proven technologies should not be more widely applied.
Minerals2014, 4(4), 815-834; doi:10.3390/min4040815 - published 18 December 2014 Show/Hide Abstract
Abstract: Consistently classified among the references for calcite simple prisms, the microstructural units that form the outer layer of the Pinctada margaritifera have been investigated through a series of morphological, crystallographical and biochemical characterizations. It is often said that the polygonal transverse shape of the prisms result from the competition for space between adjacent crystals. In contrast to this classical scheme the Pinctada prisms appear to be composed of four successive developmental stages from the concentrically growing disks on the internal side of the periostracum to the morphological, structural and compositional changes in both envelopes and mineral components at the end of the prisms. These latest structural and compositional changes predate nacre deposition, so that the end of prism growth is not caused by occurrence of nacre, but by metabolic changes in the secretory epithelium. This sequence makes obvious the permanent biological control exerted by the outer cell layer of the mantle in both organic envelopes and mineralizing organic phases.