Salt Release and Movement in Processed Oil Shale

Salts present as a component of processed, discarded oil shale represent not only a potential environmental hazard, but also a detrimental influence in the reestablishment of vegetation on processed shale disposal sites. The saline characteristics of Paraho processed oil shale were investigated in a two‐phase series of laboratory experiments. The first phase studied the release of salts from two naturally distributed shale particle sizes packed in lysimeters constructed of plastic pipe and subjected to five leaching situations. All the lysimeters were instrumented with a porous‐cup‐vacuum system that allowed periodic nondestructive sampling of the soil solution with depth and time. Electrical conductivity and specific ion concentrations were measured. The second phase of the experiments involved subjecting three particle sizes of shale to a variety of shale/water ratios. The subsequent solutions were analyzed for electrical conductivity (EC) and concentrations of Ca, Mg, Na, K, Cl, and SO 4 . The lysimeter experiments demonstrated the highly soluble nature of the salts present in the Paraho processed shale. These salts are primarily composed of Mg, Na, and SO 4 and are predominately in the precipitated form, existing external to the shale. The most efficient treatments for removing salt from the upper 60 cm of the shale were those in which large (about 0.5 pore volumes) pulses of water were applied. To reduce the EC to acceptable levels (<4.0 mmho/cm) required application of approximately 2 pore volumes of water. Results of the batch studies indicate a proportional relationship between dilution ratios and EC on a log‐log scale. Similar EC and dilution ratio relationships were observed for the cation sums. Ion analysis showed Mg and Na to be as much as 93% of the total water‐soluble cations and SO 4 to be the dominant anion.