Drenaje

ACID DRAINAGE DECONTAMINATION
THE ANDINA DIVISION CASE STUDY

Eduardo Astorga Jorquera

División Andina Codelco Chile

ABSTRACT

Today the Chilean mining industry faces the unattainable challenge of complying with the MINSEGPRES (the Chilean version of the EPA) decree regarding “Mining Contact Waters”. These waters flow from the waste rock dumps containing high concentrations of heavymetals and are often blue in color. Treatment has proven impossible to achieve due to the volume and loadings in particular of the sulphate component. No treatment technology currently exists that would enable the company to be compliant below the maximum value of 1,000 ppm (Table 1).

Along with the popular consensus that “No one is compelled to achieve the impossible” we are now at a newbeginning regarding the issue of sulphates in mining water. It is reasonable to accept that a very qualified exception must be established modifying the Supreme Decree 90/2000 (D.S. 90) from 1,000 up to 2,500 ppm of Sulphate while continuing with remediation studies to certify technological advances through pilot testing.

From mid/long range mining points of view, the only reasonable option is toincorporate special criteria that would be taken into account by the regulations.

Paradoxically, in Chile the technical feasibility of meeting the established regulatory value remains a very serious issue. The second concern arises from legal ownership, when treated water is released into water bodies belonging to independent third parties. The impossibility of compliance increases whenminimum water flows vary due to the seasonal changes.

The most viable solution, irrespective of consumption rights, is associated with the high volume periods and consists in its collection, subsequent treatment and utilization in the mining processes with and the occasional return of non-processed water to rivers and other water bodies. Thus, compliance of the secondary norm, related to irrigationis achievable without negatively affecting the receiving water body.

It is noteworthy to conclude by stating that the D.S. 90/2000 originally was enacted for industrial or commercial “establishments”, and was never intended for the mining industry.

Indeed, extraction processes with greater volumes should be considered, but under alternative guidelines and with a common sense approach.INTRODUCTION

Andina [1] Division’s mining reserves are estimated to be at least 6,000 Mtons. This represents the main source of Codelco-Chile’s mining resources, making it one of the major copper reserves worldwide. Maintaining a competitive edge in this global market requires maximising both the mining and the processing rate.
 
This is verified in the context of the copper cut off gradedemonstrating that a gradual decrease will be experienced and be counteracted with greater extraction and processing rates. Focusing on the open pit operation (exploitation) during the next three to four decades and by maintaining a rate of ~244 ktpd of ore to the concentrator, both in turn will sustain a competitive operation for more than 25 years and at the same time will triple production.
 Andina’s “Waste Rock Disposal and Drainage Management System” project aims to contribute to the long-term continuity of the operation. By using competitive rates reachable through the open pit operation and by allowing the extraction of its reserves the best economic value will be achieved. Andina Division will establish quality improvement standards with relation to the river water minimums, whileat the same time preventing future negative environmental impacts.
 
The Project scope is to design the waste rock disposal facility with a final capacity of 2,200 Mtons. It is located in the North Deposit. Also, to prevent negative impacts to the adjoining river system from the acidic drainage, a treatment system must be constructed and operated. This is a complementary project to the...