A study of factors suspected of influencing the settling velocity of fine gold particles

In this study, the authors used a radiotracer detection system coupled to a frequency counter and the radioisotope, lmAu, to investigate the effect of several variables on the terminal settling velocity of gold particles. The settling velocities of 35 manufactured gold particles (97 mg to 0.03 pg) were determined in order to produce working gold settling velocity vs. size-shape graphs for practical engineering application. Additionally, eight gold spheres were progressively flattened through 3 stages. At each flatness stage their settling velocity was determined. This highlighted the effect on settling velocity of decreasing shape factor for particles of constant mass (97 mg to 0.6 pg). The settling velocities of natural gold particles were also determined and compared to those of the corresponding manufactured particles. Finally, a generalized randomized block design was generated to explore the effects of three variables on the settling velocity of gold grains. The design was to be blocked according to gold size-shape combinations. The three variables (factors) studied were water temperature, clay concentration in the fluid, and the clay mineralogy of the suspended clays. This design was analyzed using a fixed effects analysis of variance model. The analyses show that all three factors had a significant (p < 0.001) influence on the settling velocity of gold particles. The data suggest that the clay mineralogy (viscosifying properties) of suspensions is perhaps the most influential parameter with respect to settling velocity determination.United States Bureau of Mines funded this project (Research Grant No. 1154102)