Minerals

648 KiB

Open AccessReview

Rhenium Nanochemistry for Catalyst Preparation

by Vadim G. Kessler and Gulaim A. Seisenbaeva

Minerals 2012, 2(3), 244-257; https://doi.org/10.3390/min2030244 - 14 Aug 2012

Cited by 23 | Viewed by 9951

The review presents synthetic approaches to modern rhenium-based catalysts. Creation of an active center is considered as a process of obtaining a nanoparticle or a molecule, immobilized within a matrix of the substrate. Selective chemical routes to preparation of particles of rhenium alloys, rhenium oxides and the molecules of alkyltrioxorhenium, and their insertion into porous structure of zeolites, ordered mesoporous MCM matrices, anodic mesoporous alumina, and porous transition metal oxides are considered. Structure-property relationships are traced for these catalysts in relation to such processes as alkylation and isomerization, olefin metathesis, selective oxidation of olefins, methanol to formaldehyde conversion, etc. Full article

(This article belongs to the Special Issue Advances in Rhenium Mineralogy, Geochemistry and Industrial Uses)

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993 KiB

Open AccessReview

Textural Evidence of Episodic Introduction of Metallic Nanoparticles into Bonanza Epithermal Ores

by James A. Saunders

Minerals 2012, 2(3), 228-243; https://doi.org/10.3390/min2030228 - 14 Aug 2012

Cited by 25 | Viewed by 9412

Abstract

Tertiary low sulfidation (LS) epithermal deposits in the western USA often show evidence of the former presence of nanoparticle-sized precious-metal and silica phases in the highest grade (bonanza) ores. Here, nanoparticles are defined to have a size less than ~10⁻⁷ m. The ore-mineral textures that formed from aggregation of nanoparticles (or colloids) observed to date in these ores include electrum and naumannite (Ag₂Se). Here it is proposed that chalcopyrite also forms nanoparticles in these ores, but sulfide nanoparticles apparently have significantly different physical (surface) properties than the precious-metal phases, and thus exhibit different mineral textures (e.g., no textural evidence of previous chalcopyrite nanoparticles). Textures described here show that nanoparticles of precious-metal phases and silica were episodically and often repeatedly deposited to form the banded bonanza veins typical of many western USA epithermal deposits. Chalcopyrite is the most abundant metal-sulfide mineral in these bonanza ores, and it was also deposited episodically as well, and it appears to replace earlier formed naumannite dendrites. However, this apparent “replacement” texture may just be the result of naumannite dendrite limbs trapping chalcopyrite nanoparticles that later recrystallized to the apparent replacement texture. The episodic and repetitive nature of the metal-depositing events may record periodic “degassing” of magma chambers at depth, where metals are repeatedly delivered to the shallow epithermal environment by “vapor-phase” metal (loid) transport. Full article

(This article belongs to the Special Issue Advances in Economic Minerals)

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1499 KiB

Open AccessArticle

Characterizing Frothers through Critical Coalescence Concentration (CCC)95-Hydrophile-Lipophile Balance (HLB) Relationship

by Wei Zhang, Jan E. Nesset, Ramachandra Rao and James A. Finch

Minerals 2012, 2(3), 208-227; https://doi.org/10.3390/min2030208 - 13 Aug 2012

Cited by 87 | Viewed by 12723

Abstract

Frothers are surfactants commonly used to reduce bubble size in mineral flotation. This paper describes a methodology to characterize frothers by relating impact on bubble size reduction represented by CCC (critical coalescence concentration) to frother structure represented by HLB (hydrophile-lipophile balance). Thirty-six surfactants were tested from three frother families: Aliphatic Alcohols, Polypropylene Glycol Alkyl Ethers and Polypropylene Glycols, covering a range in alkyl groups (represented by n, the number of carbon atoms) and number of Propylene Oxide groups (represented by m). The Sauter mean size (D₃₂) was derived from bubble size distribution measured in a 0.8 m³ mechanical flotation cell. The D₃₂ vs. concentration data were fitted to a 3-parameter model to determine CCC95, the concentration giving 95% reduction in bubble size compared to water only. It was shown that each family exhibits a unique CCC95-HLB relationship dependent on n and m. Empirical models were developed to predict CCC95 either from HLB or directly from n and m. Commercial frothers of known family were shown to fit the relationships. Use of the model to predict D₃₂ is illustrated. Full article

(This article belongs to the Special Issue Advances in Mineral Processing)

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1347 KiB

Open AccessArticle

Zn-Pb Ores of Mississippi Valley Type in the Lycksele-Storuman District, Northern Sweden: A Possible Rift-Related Cambrian Mineralisation Event

by Kjell Billström, Curt Broman, Jens Schneider, Warren Pratt and Göran Skogsmo

Minerals 2012, 2(3), 169-207; https://doi.org/10.3390/min2030169 - 29 Jun 2012

Cited by 19 | Viewed by 10809

Abstract

The epigenetic Zn-Pb deposits in the Lycksele-Storuman ore district, northern Sweden, are hosted by Paleoproterozoic basement near the margin of the Caledonian mountains. A paleogeographic reconstruction suggests that platform sediments, including Cambrian shales, overlaid the mineralised basement. The mineralisation type, containing sphalerite, galena, calcite and fluorite, is confined to veins and breccias and interpreted to be of Mississippi Valley Type (MVT) style. There is no appreciable wall rock alteration. Fluid inclusion work reveals coexisting aqueous and hydrocarbon fluids. Ore deposition is interpreted to have occurred during mixing of two fluids; a cool ( Full article

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Minerals, Volume 2, Issue 3 (September 2012) – 4 articles , Pages 169-257

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