SEEKING THE PHILOSPHER'S STONE: USING A MINE-TAILING LINE AS A GEOCHEMICAL REACTOR FOR TREATING ACID-ROCK DRAINAGE - BINGHAM CANYON UTAH, USA

Kennecott Utah Copper Corporation (KUCC) manages 6.8E+07 m3 of low-pH, high-sulfate, high-metals groundwater in the Jordan Valley (Utah, USA), using the active tailing disposal system as a “geochemical reactor”. KUCC evaluated the chemistry and mineralogy of tailing and pipeline scales, conducted laboratory-scale water-rock experiments, monitored the aqueous chemistry of source waters and the chemistry of both solutions and solids throughout the tailing system, and used thermodynamic calculations to evaluate specific reactions observed during experiments and monitoring.

At acidic flows up to 22 m3.s-1, the tailing system acts as a nearly ideal plug reactor, with no measurable dispersion in parameters over a 25 km reach and maintains the discharge ph at a value > 6.7. Reaction of low-pH, high-SO4 with the carbonate-based acid neutralization capacity (ANC) of the tailing slurry precipitates neutralizes the mixed aqueous stream, precipitates Fe- and Al-hydroxides and gypsum, and removes trace metals by sorption at rates ranging from 60% for Mn to > 99% for Al, Cu, Fe, and Zn. Precipitated and sorbed metals are discharged with the tailing solids to the engineered tailing impoundment at Magna. Because of the very high flux of alkaline tailing, the design-basis flows of acidic water do not deplete the ANC of tailing within the analytical precision of the measurements. By maintaining pH above 6.6, KUCC can meet all regulatory discharge limits for dissolved metals.