New Mexico Geological Society Annual Spring Meeting — Abstracts

Hydrometer analyses are performed when it is necessary to know fine particle size distribution. A glass bulb is inserted into a solution of dispersing agent and soil sample, which measures the relative density of the fluid surrounding the tip of the bulb. In conducting hydrometer analyses on rock pile samples from Questa mine, it is noticed that samples can drastically vary in behavior due to physical and chemical properties. A possible problem that could arise is the need to change the amount of dispersing agent in order to keep particles from flocculating. Early tests indicate that certain samples need more than the usual amount of dispersing agent, but that too much in turn causes additional problems.

The hydrometer method is used on fine particles because it is much easier, faster, and as accurate when compared to dry sieving. Possible problems that exist are statistical variation (inherent in sample preparation/choice) and how to determine whether to use 50 or 100 grams of sample without actually performing a dry sieve analysis, thus negating the need for the hydrometer.

Chemical composition also causes variations in particle surface forces. A phenomenon known as flocculation (clumping) was observed during certain samples’ tests, indicating the clay particles are attracted to each other. Intuitively the larger, clumped particle will now settle faster, negating Stoke’s Law, and invalidating the hydrometer analysis. We endeavor to determine ideal calgon and sample concentrations to be used for each test based on properties of the sample and if statistical variation is significant.