ANALYZING THE STRUCTURAL PROPERTIES, GEOLOGIC CONDITIONS, AND FRIABILITY OF GARNET SANDS FROM FOUR MINE SOURCES AROUND THE WORLD: IMPLICATIONS FOR THE DRY-AIR ABRASIVE SAND BLAST-CLEANING INDUSTRY

Due to its relatively high specific gravity, chemical inertness, isometric geometry, nontoxicity, lack of crystalline silica, ability to be recycled, low friability, and high hardness, garnet sand (var. almandine–pyrope) is one of the leading non-metallic abrasive media being used in the dry-air abrasive sand blast-cleaning industry. The primary task of this industry is to blast-clean steel infrastructure, remove all mill-scale and rust/corrosion, while simultaneously preparing the steel for a top-coating, which increases the integrity and longevity of the steel. Marco Industries (Davenport, IA) has provided five garnet sand samples from four localities. Two of the five samples are of hard rock origin while the remaining three samples were mined from fluvial systems. One hard rock garnet sample was mined from khondalites in the granulite belt of the North China Craton, Inner Mongolia, and the other from a meta-gabbro-derived garnet-amphibolite from Gore Mountain, New York, U.S.A. Two of the three fluvial garnet sands were mined from the Thamirabarani River feeding into Bengal Bay, Eastern India, and the other from the Hutt River emptying into Port Gregory, Western Australia. X-ray fluorescence spectroscopy, scanning electron microscopy, and grain size analysis methods were used to determine bulk and trace element compositions, change in geometry, percent degradation, percent dusting, and friability of each garnet sample. In order of increasing friability, the sample rank: 1: NY-garnet sample, 2: India (1) garnet sample, 3: India (2) garnet sample, 4: Australia garnet sample, and 5: Mongolia garnet sample. Data show that the superior garnet sand with the lowest friability is from Gore Mountain and the most inferior, highest friability, is from Mongolia. Another rank was assigned to each garnet in terms of increasing dust created during one blast operation, with particles ranging from 1 to 100 µm in diameter. India (2) garnet sand created 7.7% dust, New York garnet sand created 8.9% dust, India (1) garnet sand created 12.7% dust, garnet sand from Australia created 14.4% dust and garnet from Mongolia created 26.8% dust. The percentages show how much of the garnet sand degraded after one blast operation, and provide insight about the friability of each garnet sand.