Hydrochemistry and hydrodynamics of injecting an iron-rich pickling liquor into a dolomitic sandstone: A laboratory study

Waste pickling liquor containing high concentrations of iron salts was injected into cores of quartzite, sandstone, and dolomite in a laboratory study to determine what effect this procedure might have on the permeability of these rock types. Experiments were performed at field conditions 40°C and 13.8 MPa (megapascals) in a high-pressure triaxial chamber similar to that used in rock-mechanics testing but modified to allow downstream sample collection of effluent liquids and direct visual monitoring at in-situ conditions. Five samples were tested, ranging in effective porosity from 2.9 to 13 percent and in lithology from a quartzite to a dolomite. Hydraulic conductivity of the quartzitic samples remained unchanged during injection of over 50 pore volumes of pickling liquor, but significant decreases in the hydraulic conductivity of dolomitic samples were observed. Chemical analyses of effluents from a dolomitic sample suggest that carbonate minerals were dissolving and iron was precipitating. Clogging of pore space by CO₂ entrapment or by CaCl₂ precipitation did not seem to play a role in decreasing hydraulic conductivity because injection into a dolomitic core of more than 140 pore volumes of HCl at a concentration similar to that of the pickling liquor caused only a slight decrease in hydraulic conductivity compared with the decrease observed when an additional 30 pore volumes of pickling liquor were subsequently injected.