Product Stewardship in Wollastonite Production

Abstract

In July 2002, NYCO Minerals, Inc., discovered a heretofore unknown contaminant in its wollastonite ore. The contaminant was first believed to be tremolite asbestos. Immediate efforts were made to eliminate this material. Additional studies were initiated to fully characterize the contaminant and its distribution in the ore body. Subsequent study by NYCO and their consultants led to the identification of the contaminant as a transition material (TM) intermediate between tremolite and talc. In vitro dissolution rate measurements indicated that the TM dissolved much more rapidly than tremolite asbestos. This article provides background information on wollastonite mineralogy and NYCO's product stewardship program (PSP). At present, NYCO Minerals uses selective mining to control the trace levels of TM in the ore and finished product verified by periodic monitoring of workplace air and finished product.

This research was supported by NYCO Minerals, Inc. However, the findings and conclusions are those of the authors and not necessarily those of NYCO Minerals, Inc. We acknowledge the kind assistance of Dr. Bruce Zoitos of Unifrax Corp. in making the durability measurements and the useful insights and thoughtful comments on this article by Dr. Richard J. Lee and Drew R. Van Orden of the RJ Lee Group, Inc. The support of numerous personnel from NYCO Minerals in collecting the samples and RJ Lee Group, Inc. in their analyses should also be acknowledged as well as the assistance furnished by MSHA personnel. Portions of these results were presented at the Industrial Minerals Association—North America (IMA-NA) spring meeting, April 25–27, 2007, Washington, DC. All uniform resource locators (URLs) were valid as of 15 June 2007.

Notes

*For a discussion of this point, see the proposed rule on the asbestos exposure limit (70 Federal Register, No. 145, pp. 43950–43989 and especially 43954). On June 8, 1992 OSHA (see 57 Federal Register 24310–24311) deleted the nonasbestiform types of these minerals from the scope of its asbestos standards. OSHA found insufficient evidence that nonasbestiform actinolite, tremolite, and anthophyllite presented “a risk similar in kind and extent” to their asbestiform counterparts.

†As shown later in the text, the material initially thought to be “tremolite asbestos” was actually misidentified. Quotes are used to indicate the uncertainty of the identity of the material.

*The mean squared error (MSE) of the difference between x_t and S_t values is a function of the smoothing parameter α. In this example, the MSE is minimized for a value of α of .34. However, the MSE function is very flat in the vicinity of the optimum, so that the value of the MSE function at an α of .2 is little different from that at .34. In any event, choice of a higher smoothing constant will have the effect of lowering the forecast tremolite concentration in the later time periods as the majority of these observations are at the LOD. The intent of plotting the smoothed values is to illustrate the point that in the later months, concentrations approach the LOD.

*A useful explanation of electron diffraction can be found at http://nvl.nist.gov/pub/nistpubs/jres/106/6/j66ben.pdf.

†See, e.g., http://minfile.gov.bc.ca/Summary.aspx?minfilno=092GNW052, http://www.em.gov.bc.ca/DL/ArisReports/07257.PDF, http://www.amonline.net.au/geoscience/earth/metamorphism.htm, http://franklin-sterlinghill.com/dunn/ch17/wollastonite.stm, and http://www.und.edu/instruct/mineral/geol318/webpage/kanupuru/.

^§ Defined as “Of or relating to something that has survived, as structures or minerals after destructive processes.”

*A field-emission cathode in the electron gun of a scanning electron microscope provides narrower probing beams at low as well as high electron energy, which enable both improved spatial resolution and minimized sample charging and damage. FESEM produces clearer, less electrostatically distorted images with spatial resolution down to 1.5 nm, some 3 to 6 times better than conventional SEM.

*See, e.g., http://www.assomineraria.org/news/attach/speech_odriscoll.pdf, http://mpra.ub.uni-muenchen.de/2214/01/MPRA_paper_2214.pdf, http://www.mineralsuk.com/britmin/economic_importance_of_mins.pdf, http://www.imaeu.org/fileadmin/downloads/publications/articles/LegEyeMay05.pdf, http://www.csiro.au/news/ps2pi.html, and http://minerals.usgs.gov/east/industrial/index.html.