Having non-ferrous metals without having a mine

A new method of electrowinning leads to much lower rates of impurities in the recycling of non-ferrous metals.
Rainer Sturm, pixelio.de

43,000 years ago, in what is now Swaziland, the man struck into soil for the first time in search for hematite. The site is today called “The Lion Cave” and is the oldest archeological finding of human mining activity. While it is certain whether this is the oldest mine in the world, what is certain is that mining has greatly changed since then and that it has also greatly shaped human civilization. However, it is also now time to turn to methods of obtaining resources that operate without the great environmental impact of mining, especially in the area of non-ferrous metals which are used more and more in the world.

Mining of today is a complex activity of many stages and specific practices will depend on the properties of the ore mined. In this section, we will examine the contemporary methods for obtaining non-ferrous metals through mining. Non-ferrous metals can be extracted from open pits as well as from underground mines, sometimes even from both of them in combination. The most often mined metals are copper, zinc, aluminum, lead and noble metals with various industrial applications. The simplified overview of the process goes as follows. First of all, the ore needs to be extracted from the ground. Depending on the location and the metal, the concentration of the said metal can vary greatly, going from 0.5-1% for copper to 8.8% for aluminum (10g per kg and 88g per kg respectively). Once when the ore is extracted, it needs to be separated into valuable metals from other impurities (also called gangue).

All of the extraction processes can be put into three main categories. These are pyrometallurgy, hydrometallurgy and electrometallurgy. As these names suggest, these process will mainly use fire and high temperatures, water-based solutions, or electricity for separating the valuable materials from the gangue. For example, the main extraction process of pyrometallurgy is called smelting. In smelting, heat combined with a reducing agent is used to separate the valuables and the gunge in the ore. The removing agent is usually carbon-releasing material, such as coke for example. The carbon can remove the oxygen from the ore and it leaves behind the metal that can find its later industrial application. Hydrometallurgy and electrometallurgy both operate with the same end-goal in mind, but achieve it through different means. However, the topic and the scope of this article do not allow for going into greater detail here. It is important to point out that this has been greatly simplified and that there are many more stages and factors at play than the above listed.

As it can be assumed based on the numbers relating to concentration of metals in the Earth’s surface, mining leaves behind a lot of waste material. Let us imagine a copper excavation locality with the concentration of 1%. This means that there will be at least, if not more than, 9,900kg of waste material, which can have serious consequences for the environment. Since the material in question here are non-ferrous metals, this means that the waste material will most likely be piled up rock and earth. One of the common threats from such piles is the so called acid rock drainage. The waste rock very often contains pyrite, an iron sulfide. Pyrite is a dangerous substance because it can acidify water that comes into contact with it, enabling it to dissolve materials such as copper, zinc or silver. This acidic combination of pyrite is water specifically is what is called acid rock drainage. If left uncontrolled, acid rock drainage can contaminate underground water streams or nearby rivers, rendering the water bad for drinking and impossible to use for irrigation. Air contamination is also very common around areas where the aforementioned process of smelting is being conducted. This happens because the process requires large quantities of carbon monoxide, and because it emits sulfur dioxide. High concentrations of sulfur dioxide in the atmosphere mean that sulfur dioxide combines with water, finally making an acidic combination that gives us the so called acid rain which is very detrimental to all life forms. These are only two the common and most dangerous forms of environmental pollution, there are many more which also would not fit into this article, but that are nevertheless very important and dangerous.

Since there is a vast amount of non-ferrous metals in circulation right now for various applications, a lot of it can be obtained through recycling. The super power of non-ferrous metals is that they can be recycled infinite number of times without losing their initial properties that made them useful across various industries. The chief method of obtaining non-ferrous materials from impure compounds, ores or waste is electrowinning. When the methods is used for non-ferrous metal extraction for the purpose of recycling, the process goes as follows. First of all, the waste material is put into a liquid solution where it is dissolved through the process known as leaching. What remains when the material is dissolved is a liquid called electrolyte, which is a conductive solution formed by dissolving positively and negatively charged ions. There are also two electrodes submerged into the solution; a positively charged anode and a negatively charged cathode through which the electric current will be run. When the current is run through the solution, the positively charged cations will move towards the cathode, and the negatively charged anions will move towards the anode. For example, in the case of electrowinning copper from copper sulfate, copper sulfate will dissolve into positively charged copper ions negatively charged anions. When electricity is applied, copper will move towards the cathode and get plated on it, but, there is a problem. As the concentration of copper starts to decrease in the solution, other materials start to plate onto the cathode resulting in impurities. Emew Corporation, however, has found a solution to this problem. In Emew electrowinning, the electrolyte is sent at high speeds through a cylinder consisting on the outside of a cylindrical cathode and on the inside of a cylindrical anode. This results in much lower rate of impurities in the end product. In fact, emew electrowinning technique enables us to produce recovered copper of 99% purity, a significantly higher mark from conventional methods. With such high purity rates, the reliance on mining is greatly reduced as there is much more copper to recovered from the already existing materials.

The advances made in recycling and metal recovery technologies have truly shown the way it is possible to increase metal producing capacities without increasing our existing carbon footprint or leaving a metaphorical footprint of rust, acid and misshapen landscapes.

1 COMMENT

  1. Great article. I work in the mining industry but I am also environmentalist with experience in natural resources and biology. I do agree that it is important to recycle mined metals such as copper and aluminum to help conserve our natural environment. Although, a tremendous amount of energy also goes into recycling processes of metals. It would be interesting to compare the ratio of energy to usable product that goes into mined vs. recycled metals. Thanks!

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