| Abstract: | The interaction of contaminated rocks (loam and clay recovered from depths of 1 and 4 m by a borehole drilled in the territory of a metallurgical plant in Ryazan oblast) was examined experimentally, and the concentrations (C) of twenty elements in solutions after the experiments were analyzed. The concentrations lie within ranges typical of the upper aquifer in the contaminated area, with the Al, As, Mo, Na, S, and W concentrations exceeding the maximum permissible concentration values (MPC). The experiments with clay yielded less stable and unambiguous results because a certain portion of clay particles passed through the filter (0.05 μm) when the rock and water were separated after the experiments and thus may contribute to the concentrations of certain elements in the solutions. The experiments led us to derive two types of dependences for each element: (1) C-t (time) dependences within the range of 1–36 days and (2) C-n (number of acts of rock treatment with fresh water portions) dependences. The both types are presented by various mass ratios of rock and water (r/w = 0.5 and 0.1). The character of the dependences led us to classify the elements into two groups. The concentrations of elements of one of the groups (As, Si, and V) shows no systematic dependences of C on t, n, and r/w, and this corresponds to equilibrium reached by fast adsorption-desorption reactions. These dependences in the other group of elements (almost all other elements) testify that the slow dissolution-precipitation reactions proceed away from equilibrium. The C-n dependences were utilized to evaluate the recovery ratios of elements and to identify easily soluble species of Ca, Mg, Mo, Na, S, and Sr. A fraction of ooliths (goethite + SiO2) separated from the clay contains elevated concentrations of certain trace elements. Microprobe analyses of the ooliths show that elements whose concentrations are comparable with the detection limits of microprobe analysis are evenly distributed, with elevated concentrations detected only in two instances: (i) Ce and La (in monazite) and (ii) Co and Ni (in MnO). Having a high isomorphic capacity with respect to several elements, goethite can act as a geochemical barrier and thus constrain the migration of these elements. The correlation dependences of elemental concentrations in rock fractions were utilized to derive further information on the speciation of the elements related to common sources in various rocks and the number of concentrator minerals. |
