Reclamation of Acidic Copper Mine Tailings Using Municipal Biosolids

Reclamation of copper mine tailings in a cost effective, successful, and sustainable manner is an ongoing area of evaluation in the arid southwest. A study was initiated in September, 1996 near Hayden, Arizona to evaluate the use of municipal biosolids for reclaiming acidic copper mine tailings (pH of 2.5 to 4.0). The main objectives of the study were to I) define an appropriate level of biosolids application for optimum plant growth, and 2) evaluate the effects of green waste and lime amendments. The experiment was a randomized complete block design with four biosolid rates of 20, 70, 100 and 135 dry tons/acre (45, 157, 224, 303 Mg/ha), three amendment treatments (none, green waste, and green waste plus lime); with three replications. Non-replicated controls (no treatment, green waste only and lime only) were included for comparison. Shortly after biosolids incorporation to a depth of 10-12 inches (25.4-30.5 cm), composite soil samples (0-12 inches) of each plot were taken. Biosolids incorporation increased the pH of the tailings (>5. 75) and additional increases in pH were noted with lime application. In January 1997, the plots were seeded and sprinkler irrigation was commenced. A total of 4.47 inches (11.4 cm) of rainfall and 3.8 inches (9.7 cm) of irrigation were applied until harvest in May 1997. Data from the first growing season indicates optimum growth (>66 lbs/acre or >74 kg/ha) at biosolids rates of 70-100 dry tons/acre. There was a significant positive effect on growth of green waste and lime amendments. Surface NO,-N concentrations in biosolids amended plots were greatly reduced (from 23 to 6 mg/kg) by addition of green waste. There was no evidence for N0 3 -N leaching below 12 inches (30.5 cm).