Characterization of sand processed for use in hydraulic fracture mining

Each hydraulic fracturing well uses up to 5,000 tons of silica-containing sand, or proppant, during its operational lifetime. Over one million wells are currently in operation across the continental United States. The resulting increase in demand resulted in the production of 54 million metric tons of sand for use as hydraulic fracturing proppant in 2015.

The goal of this study was to determine whether mining, processing, and transport facilities handling proppant sand create a comparison between risk of exposures to crystalline silica and respirable dust. Samples of unprocessed, or “raw” sand, and processed sand were aerosolized in an enclosed chamber. Respirable dust samples were collected from the chamber and subjected to gravimetric and x-ray diffraction analysis.

Percentage of silica composition was compared between bulk and respirable samples from the same sand type. In order to simulate potential respirable particle production from stress during transport, some processed sand samples were submitted to low frequency vibration before being aerosolized.

Higher concentrations of respirable dust were observed when raw sand was the generation source, whereas processed dust contained higher percentages of respirable crystalline silica at lower concentrations of respirable dust. When vibration was introduced prior to aerosolization, concentrations tended to increase as vibration times increased. Results of the study indicate that workers in sand mines and workers exposed to proppant that has undergone low-frequency vibration are at increased risk of exposure to respirable crystalline silica compared to workers who are exposed to proppant that has not undergone vibration.