English

Abstract

Since 2001, Somincor have been investigating the feasibility of changing the tailings deposition method to sub-aerial placement of paste at its Neves Corvo Mine in southern Portugal. The pyritic tailings have a very high acid generation potential and are currently being placed sub-aqueously in a conventional tailings facility. Work completed to date has included a laboratory bench-scale screening program, a three-year field cell monitoring program, and pilot plant testing to investigate deposition techniques, co-disposal with acid- generating waste rock and cover performance. This paper describes the results of the field cell study and provides an introduction to the ongoing pilot plant testing. Although the field cells exhibited short-circuiting of seepage, the field cell monitoring program has demonstrated that a considerable lag time exists before acidic seepage is generated. This lag time has important consequences in terms of operational placement of paste and closure of a paste deposit. Based on geochemical modeling and observations from the bench-scale testing program, long-term seepage quality may reflect buffering by kaolinite. A pilot plant paste program has been ongoing since February 2005. This large-scale test (a 1-hectare site containing 35,000 m 3 of paste) provides an exceptional opportunity to investigate paste deposition techniques. In addition, co-mixing with waste rock will be evaluated, as well as the long-term environmental stability of the paste. After paste deposition has been completed, the pilot area will be capped using several trial covers and its geotechnical and environmental performance will be monitored.