Solving mine water problems with peat-based sorption media - Case study

ABSTRACT

Mine water often contains trace metals that must be removed prior to discharge. Conventional technologies exist but generally are labor intensive and expensive. Peat-based sorption material can be a less expensive alternative and is easily deployed in either “semi-active” or passive treatment designs. The media is a hardened uniform granular material produced from reed sedge peat. It has a hydraulic conductivity of around 1 cm/sec, metal removal capacities ranging from 1 - 15% dry weight and been used successfully to remove suspended and dissolved metals from the Soudan iron mine in Minnesota and base metal mines in North America. 

In November 2012, a pilot test was initiated at the Soudan mine. Since startup, over 62.4 million liters (> 32,000 bed volumes) have been treated with an average removal of around 75% for suspended copper and 60% for dissolved copper. Backwash is required at about 4000 bed volumes, but with a combination of air sparging and high flow backwash, the suspended material is effectively removed from the bed. The APTsorb media produced equivalent removal to the existing system but reduced the size and complexity of the system and reduced operating costs by 50%.

In October 2013, a pilot test began at a base metal mine in North America. The pilot was designed to model both a “semi-active” (pressurized tank) and passive (biocell) treatment system approach. Lead removal in both pilot systems was generally greater than 99%. Excessive solids in the mine discharge contaminated the pressurized tank and affected treatment at 6400 bed volumes. This reduced dissolved metal removal efficiency in the media from 99% to about 85% and caused the discharge to exceed the permit limit of 11.5 ug/l lead. The biocell was not affected and it continued to meet discharge limits up to 20000 bed volumes.

Keywords: Copper, lead, zinc, cadmium, ion exchange, passive treatment, adsorption,