(452d) Treatment And Reutilization Of Liquid Effluents Of Copper Mining In Desert Zones

This study investigated the different methodologies for the treatment of mining effluents and their use in the Chilean mining industry. The technologies compared were selected by the International Network for Acid Prevention as the best available techniques to treat sulfates - the most important copper mining wastewater contaminants. Some of these techniques have technical and commercial possibilities (potential) to treat such effluents, especially effluents contaminated with heavy metals such as copper. The treatment technologies analyzed involved Physico-chemical methods such as Precipitation; Membranes; Ionic Exchange and Biological reduction using Bioreactors or Artificial Wetlands. The results of the comparison led us to conclude that only precipitation with Lime and Reverse Osmosis are used in Chile. The biological reduction of sulfates using Bioreactors was implemented only on a pilot scale. The study also revealed that more than 50% of the seventeen largest Chilean mining companies treat their effluents using several techniques such as Gravity Separation, Neutralization and Sedimentation, Separation and Controlled Oil Disposal, Filtration and Evaporation, Removal of Suspended Solids, Ion Abatement and Dissolved Air Flotation.

The Acuerdo de Producción Limpia (Clean Production Agreement), signed in 2002 by the Chilean government and the mining sector, identified technologies that could be applied for optimizing the consumption of water. Within this framework, a study published in 2004 whose results were presented in PROCEMIN (2004) reports that at least eleven technologies are applicable in the Chilean mining context. Among them, only some have been classified as the best available techniques (BAT) by the INAP report (2003). The study assumes that through the application of these technologies, the water consumption could be reduced to less than 0.5 m3/t in treated ores during the concentration process, and 0.25 m3/t in acid leached treated ores.

The technologies were classified into high, medium or low degree, according to their possible application. Among the high degree of applicability, Automatic Control of the Thickening Process, Recirculation of Water from Remote Reservoirs, Filtering of Washings and Deep Thickening are mentioned. Among the medium degree of applicability, Bio-remediation Treatment of effluents, Permanent Monitoring of Consumes, Dry Crushing and Pneumatic Centrifuging are mentioned. Among the low degree of applicability, Drainage Control of Lixiviation Heaps, Mine Consumption Optimization, Blowing and Extraction from the Aquifer of Washing Reservoirs and Porous Tubes are mentioned.

Technologies with a high degree of applicability require investments which range between 20kUS$ (Automatic Thickening Control) to 800kUS$ (L/s) (Deep Thickening). This requires operating costs of approximately 0.3cUS$/m (Recirculation of Water from Remote Reservoir which only applies to works with different heights above sea level and great distances between the reservoir and the thickener), to about 5cUS$ (Automatic Thickening Control, demanding a huge quantity of high cost consumables such as flocculants, energy and maintenance). Other technologies were catalogued as medium to low applicability mainly due to their high implementation costs, difficulties in their application relating to workplace characteristics (particularly due to their age), or because the technology had been applied only on a pilot scale.

Regarding treatment methods in use, the same study indicates that 56% of the 17 biggest company workplaces (each members of the Chilean Mining Council) perform treatment of wastewaters. Up to 67% of the effluents are treated, stored, or re-circulated back to the process. There is no data about the remaining 33%. The main treatment methods used are Gravity Separation, Neutralization and Sedimentation, Oil Separation and Controlled Oil Disposal, Filtration and Evaporation, Removal of Suspended Solids, Ion Abatement and ADF.

Therefore, according to the collected data framework and analysis, it could be concluded that within the Chilean mining context, there is an improvement in the use of effluent treatment technologies. The re-usage of water can also be confirmed. However, these are isolated initiatives and the justification of such initiatives is necessary in order to enhance the availability of this resource due to the difficulty or impossibility of incorporating new sources into the production process, especially in the northern zone. This affects the copper mining industry and its expansion potential, evident by the increase in the price of copper last year. From a business standpoint, this is becoming an increasingly urgent issue.

Most companies repeatedly reuse wastewaters until it loses it`s characteristics. At this stage the water is stored in ponds. The possibilities of using this water for other purposes such as irrigation are limited. For example, in Codelco's Northern Division, the water consumption in 2003 and 2004 reached about 55 millions m3, with more than 80% reuse and/or recycling, and 6% disposal (the rest is lost mainly through evaporation and water content of the product). This represents more than 3 million m3/year, or the equivalent of 15% of the gross demand for irrigation in Region 2; a demand that will reach 20 million m3 in 2017 according to the Dirección General de Aguas (2004). It is important to stress that Codelco reached levels above the mean, in relation to water use efficiency.

The adoption of treatment technologies generally requires infrastructural facilities, changes in productive processes and ad hoc managing systems. All of them need strong financial investment, which reduces their applicability in the Chilean mining context. Meanwhile, companies that consider water a scarce resource are not yet prone to invest in treatments for reusing water beyond its own immediate use.

Key words: copper mining, liquid effluents, effluent treatment.