Is the waste from extracting further copper /molybdenum from mine tailings environmentally safer than inputs?
December 17, 2009 by
Filed under copper mine
I am an investor in Amerigo Resources, a company that has a plant in Chile to extract more copper and also molybdenum from old and fresh mine tailings (from Coldeco’s El Teniente mine). They have a consultant studying laundering the waste product by a pipeline from the extraction (which involves crushing) process back into a swampy area (the Colihues) where the old tailings are stored. Apparently, the redeposited material would have the quartz removed and be more granular (crushed).
Is there a net environmental problem or benefit from this kind of recycling from and back into the Colihues tailings dam? What are the consequences of replacing the old (and some new) tailings in the Colihues with the original tailings pulled out of there with the processed tailings in more granular form after pulling out more copper and also moly?
The Chilean government is very vigilant these days about anything from mining that might pollute the environment.
I’m not sure if the main mining company, Coldeco, is using the leach-solvent extraction-electrowinning process or, SX/EW Process for their primary extraction. Amerigo Resources does a second pass on old mine tailings, which were perhaps created in the Colihues tailings dam over 20 years ago. I know that they grind those old tailings in a low-tech kind of operation.
They want to pull the old tailings out of the Colihues tailings dam, process them to extract further copper (and molybdenum), and then put what is left from their operation back into the same Colihues tailings dam. But, Coldeco (owned by the Chilean government) won’t allow this kind of recycling yet, until they are sure that a pollution problem is not created.
Do you know why laundering the waste product from Amerigo’s operations would result in pollution, meaning, I think, pollution of the Colihues tailings dam, to which most of the materials would be returned after processing?
Conventional Copper Extraction
Conventionally, copper is recovered by a pyrometallurgical process known as smelting. In this process copper ore is mined, crushed, ground, concentrated, smelted and refined. The mining, crushing and grinding portions of the processing are extremely energy intensive since the rock must be reduced essentially to talcum powder fineness in order to separate the copper-bearing minerals from it. To be applicable to this process, the ores must contain copper minerals in sulfide form; as mineral such as Chalcocite (Cu2S), Chalcopyrite (CuFeS2) and Covellite (CuS) . In the concentrating operations these minerals are separated from the gangue material of the ore, that might contain as little as 0.5% copper to form a concentrate containing 27 to 36% copper. In the smelting operation, the concentrate is fed to a smelter together with oxygen and the copper and iron sulfides are oxidized at high temperature resulting in impure molten metallic copper (97 to 99%), molten iron oxide and gaseous sulfur dioxide. The impure copper is then purified by electrolytic purification to 99.99% pure copper while the iron oxide is disposed of as slag.
Typically, in this process there is more sulfur dioxide produced by weight than there is copper. Rather than discharge the sulfur dioxide into the air, as was once the practice, the sulfur dioxide is captured and converted into sulfuric acid. In the United States, smelter-produced sulfuric acid amounts to approximately 10% of total acid production from all sources. Prior to the mid-1980s, this by-product sulfuric acid had to be sold to other industries, often at a loss due to the long shipping distances.
Beginning in the mid 1980s a new technology, commonly known as the leach-solvent extraction-electrowinning process or, SX/EW Process, was widely adopted. This new copper technology utilizes smelter acid to produce copper from oxidized ores and mine wastes. Today, worldwide, approximately 20% of all copper produced is produced by this is process. In Latin America, the total is closer to 40% whereas in the United States the total is approaching 30%.