The acid drainage generated in mining waste dumps is one of the greatest environmental and economic challenges facing the mining industry.
So much so that the current mining closure law, which seeks to ensure the chemical stability of facilities, requires mining companies to consider almost perpetual treatment to prevent the pyrite oxidation process from contaminating water and crops.
This acid drainage is caused by sulfide minerals, primarily an iron-sulfur mineral called pyrite. When pyrite encounters water and oxygen—and sometimes bacteria—it oxidizes and generates acid drainage that contaminates the surface and groundwater, seriously endangering crops, flora, fauna, and even human health.
In search of solutions to this problem, the Environmental Rehabilitation and Ecosystem Dynamics team at SMI-ICE-Chile is working on a pyrite microencapsulation project, which includes testing in the UDD C+ Center laboratory and also in a pilot plant specially developed for this project.
«We’re looking to stop this acid drainage process and avoid the enormous associated costs of the current treatment commitment,» explains Dr. Jacques Wiertz, who leads the team developing this project, along with Dilan Campos, Marcela Calderón, and Dr. David Rubinos.
“We believe that the technology we are testing will slow and eventually prevent this pyrite oxidation process that generates this acid drainage, significantly shortening the treatment application time, or even eliminating this costly need,” emphasizes Jacques Wiertz. “The goal is to create a barrier to prevent oxygen and water from coming into contact with the pyrite and causing acid drainage, also known as pyrite weathering.”
The proposal is based on the doctoral thesis “Phosphate-induced hydrogeochemical stabilisation of sulphidic lead-zinc tailings for rapid phytostabilisation”, completed by Felipe Saavedra-Mella for the University of Queensland in 2018.
Although it has already been researched, this development has yet to have large-scale applications. This is what the SMI-ICE-Chile team is working on.
Dilan Campos explains the technology’s design and its pilot-scale implementation: «It consists of a series of barrels loaded with ore containing a high percentage of pyrite, which we have already performed a mineralogical and chemical analysis on in the laboratory,» he explains. «Based on this data, we define the reagents—chemical solutions—that we will add to the rock through a drip irrigation system, so that it reacts and generates a passivation layer on the pyrite, hopefully protecting it from contact with water and oxygen. A favorable result would be that the leachate we recover is low in sulfate, has a pH close to neutral, and no metals are released.»
Watch here an animated video of some moments of this work
