Lucky Friday | processing
The ore produced from Lucky Friday is processed in a conventional flotation mill, which produces both a lead concentrate and a zinc concentrate. In 2011, ore was processed at an average rate of approximately 905 tons per day. During 2011, mill recoveries totaled approximately 93% silver, 93% lead, and 87% zinc. All silver-lead and zinc concentrate production is shipped to Teck Cominco Metals Limited’s smelter in Trail, BC, Canada.
There are three main phases to the milling process: grinding, flotation, and filtration.
grinding – the reduction phase
Grinding is the reduction of the mined ore from an average size of 9” (225mm) to an average size less than 50µm (50microns or .05mm). The main purpose of the grinding process is to liberate the various components of the ore. A 9” lump of ore is a combination of some rock, some zinc, some lead, some silver and some gold. By grinding that lump down to particles of 50µm we aim to produce particles of rock, zinc, lead, silver, or gold. Water is added during the grinding phase to suppress dust and to help pump the material around the mill.
flotation – the separation phase
Flotation is the separation of the particles produced during the grinding phase. The ground ore and water is passed through a series of cells which selectively float the zinc particles and lead particles to produce a zinc concentrate and a lead concentrate. Tailings from the process streams can be filtered and stored for use as mine backfill, or pumped to the tailings storage facility for permanent disposal in a lined tailings pond.
Filtration is the extraction of the water from the concentrates and tailings. All of the mill products are filtered to produce a dry cake with a moisture content of around 8%. The filtered concentrate is easy to handle and ready to be shipped off to smelters around the world to be turned into metal.
