AMD is a recognized significant environmental aspect in mine operations. At RRPP, control at source, prevention of migration and treatment are the three main mitigating measures employed for effective AMD management.

Control at source. The primary source of AMD from the mine operation are the ore and waste containing sulphides which are acid forming in the presence of oxygen and water. RRPP follows the accepted best practice of controlling AMD generation through inhibition of reaction of sulphide minerals with either oxygen or water, or both.

At the Tailing Storage Facility (TSF) , which is an impounding facility for tailings from the process plant and water from the pit, at least two (2) meters of water column over the tailings deposited at the Tailings Storage Facility (TSF) are maintained to inhibit reaction. Initially, the sulphides will react with the available oxygen in water but once consumed, reaction stops. Oxygen content in water is 25,000 times less than in air. Buffering from the high alkalinity of the tailings (pH 9-10) also helps in controlling AMD at the TSF.

In addition, the PAF materials used to build up the TSF is encapsulated by impermeable clay up to the final elevation.

Prevention of Migration. Another strategy used by the project to control AMD is to prevent migration of silt or suspended solids that may contain sulphides from runoffs from the exposed PAF while dam build up is active and continuing. This is done by the use of silt restraining structures such as gabions and silt fences. Three (3) sedimentation ponds also allow settling of these silt.

An old exploration adit used prior to RRPP’s operation which discharges AMD to one creek, Pagcolbon Creek, was diverted in 2007 through pipelines to one of the sedimentation ponds.

Treatment. In addition, RRPP uses both passive and active treatment facilities to also effectively reduce the acidity of the water through reaction with lime. Anoxic limestone drains and a mechanized lime mixing tank and filtration system reduce acidity of discharge from the ponds.

As final mitigating measure, RRPP is the first in the country to use the wetlands filtration system which is planted with acidity-reducing species such as cattails (Typha augustofolia), tambo (Phragmites karka, vetiver grass (Vetiveria zizanoides), and torpedo grass (Panicum repens). These plant species are proven to reduce acidity and trap dissolved trace metals in waste water.

AMD MANAGEMENT

PAF Encapsulation

Tailings Storage Facility / Dam Build Up As Designed

Wetlands

Treatment