Next Article in Journal / Special Issue
Identifying the Presence of AMD-Derived Soil CO2 in Field Investigations Using Isotope Ratios
Previous Article in Journal
Uncertainty Representation Method for Open Pit Optimization Results Due to Variation in Mineral Prices
Article Menu

Export Article

Open AccessArticle
Minerals 2016, 6(1), 16; https://doi.org/10.3390/min6010016

Porosity and Permeability of Round Top Mountain Rhyolite (Texas, USA) Favor Coarse Crush Size for Rare Earth Element Heap Leach

1
Department of Geological Sciences, The University of Texas at El Paso, El Paso, TX 79968-0155, USA
2
Texas Rare Earth Resources, 539 El Paso St., Sierra Blanca, TX 79851, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Samuel Frimpong
Received: 31 December 2015 / Revised: 3 February 2016 / Accepted: 17 February 2016 / Published: 24 February 2016
(This article belongs to the Special Issue Frontiers of Surface Mining Research)
Full-Text   |   PDF [4626 KB, uploaded 24 February 2016]   |  

Abstract

Water-saturation porosity and dye-penetration permeability measurements of Round Top Mountain rhyolite confirm that a ½-inch (13-mm) crush size would permit efficient acid heap leaching of yttrium and heavy rare earth elements (YHREEs) hosted in yttrofluorite, a YHREE-substituted variety of fluorite. Laboratory acid leaching has extracted up to 90% of the YHREEs. The bulk insoluble gangue mineralogy of the rhyolite, 90% to 95% quartz and feldspars, assures low acid consumption. Different crush sizes were weighed, soaked in water, and reweighed over time to determine water-penetration estimated porosity. Typical porosities were 1% to 2% for gray and 3% to 8% for pink varieties of Round Top rhyolite. The same samples were re-tested after soaking in dilute sulfuric to simulate heap leaching effects. Post-leach porosity favorably increased 15% in pink and 50% in gray varieties, due to internal mineral dissolution. Next, drops of water-based writing ink were placed on rhyolite slabs up to ~10 mm thick, and monitored over time for visual dye breakthrough to the lower side. Ink penetration through 0.5 to 2.5-mm-thick slabs was rapid, with breakthrough in minutes to a few hours. Pink rhyolite breakthrough was faster than gray. Thicker slabs, 4 to 10 mm, took hours to three days for breakthrough. Porosity and permeability of the Round Top rhyolite and acid solubility of the yttrofluorite host should permit liberation of YHREEs from the bulk rock by inexpensive heap leaching at a coarse and inexpensive nominal ½-inch (13-mm) crush size. The rate-limiting step in heap leach extraction would be diffusion of acid into, and back-diffusion of dissolution products out of, the crushed particles. The exceptional porosity and permeability that we document at Round Top suggest that there may be other crystalline rock deposits that economically can be exploited by a coarse-crush bulk heap leach approach. View Full-Text
Keywords: heavy rare earth elements; yttrofluorite; heap leach; yttrium; dysprosium; YHREE; rhyolite; Round Top heavy rare earth elements; yttrofluorite; heap leach; yttrium; dysprosium; YHREE; rhyolite; Round Top
Figures

Figure 1

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
SciFeed

Share & Cite This Article

MDPI and ACS Style

Negron, L.; Pingitore, N.; Gorski, D. Porosity and Permeability of Round Top Mountain Rhyolite (Texas, USA) Favor Coarse Crush Size for Rare Earth Element Heap Leach. Minerals 2016, 6, 16.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Minerals EISSN 2075-163X Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top