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Availability and Plant Uptake of Trace Elements from Recarbonated Retorted Shale¹

ABSTRACT

One solution to the management of retorted shale (spent oil shale) is to establish a satisfactory vegetative cover over retorted shale disposal piles. However, the high alkalinity of these waste materials severely hampers direct revegetation efforts. A sample of Lurgi-Ruhrgas (Lurgi) retorted shale was recarbonated to lower its high alkalinity, by exposing it to 0.04 MPa CO₂(g) and moisture for 4 d. A preliminary greenhouse experiment was conducted to examine the uptake of microelements by tall wheatgrass [Agropyron elongatum (Host) Beauv.] grown on this recarbonated shale. Exposing spent Lurgi shale to pressurized CO₂(g) and moisture lowered the pH from 11.6 to 8.6 and increased the electrical conductivity (EC) from 4.7 to 15.8 dS/m. Lowering the pH through recarbonation increased ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA) extractable Fe, Zn, Cu, Mo, and Ni, while extractable B, Sr, Cr, and Mn were decreased. Wheatgrass seeds failed to germinate in spent Lurgi shale, which had no soil cover. Plant growth decreased in the recarbonated shale compared to retorted shale with a soil cover due to higher salinity. Plant tissue grown on the recarbonated shale accumulated lower concentrations of As, Se, Ba, Cd, Sr, and Ti than did plants grown on spent Lurgi shale with a soil cover. Boron concentrations ranged from 7.2 to 13.0 mg/kg in plant tissue, with the lowest concentrations coming from the recarbonated shale. Fluoride concentrations in plant tissue increased with recarbonation but were below the toxic level. Plant uptake of Mo increased with recarbonation. The Cu/Mo ratios of the tall wheatgrass were below 2:1 in all treatments except the control. This preliminary study shows that recarbonated spent shales can be revegetated directly without a soil cover but that some leaching may be advantageous.

Key Words: high alkalinity • revegetation • stabilization • toxic elements • Agropyron elongatum (Host) Beauv.

¹ Funding was provided in part by DOE Grant no. EV/04018-9.

² Former Graduate Research Assistant and Professor, respectively, Dep. of Agronomy, Colorado State Univ., Fort Collins, CO 80523. Senior author is currently Postdoctoral Researcher, Dep. of Geology and Geophysics, University of Wyoming, Laramie, WY 82071.

Received for publication July 22, 1986.