Minery produces acid water (called AMD or ARD)
Natural Acid Rock Drainage (ARD) is amplified by mining activities. Acid water (AMD) produced by minery needs further treatment
AMD or Acid waters from mining originate through the chemical and biological oxidation of pyrite (among other materials which happen to be rich in sulfide minerals). This phenomenon occurs when rocks containing these sulfides come in contact with air or water. In addition, acid water coming from rocks and minerals includes numerous dissolved metals that add an important toxicity to the effluent.
Thus, the acidic drainage that is produced in underground and open pit mines is one of the principal sources of contamination of both surface and groundwater that are found in the mining environment.
To avoid this environmental damage, measures must be taken, both preventative (or passive) and active through the implementation of treatment methods for these acidic effluents.
In regards to treatment technologies, it is important to note that on numerous occasions a single procedure does not prove sufficient, resulting in the necessity for a combination of various procedures. Everything depends on each case and its many variables.
Note: Acidic waters are those with pH lower than 7, you may read these educational notes on pH.
That said, main treatment technologies for AMD/ARD are:
- Physio-chemical and biological processes
- Evaporation ponds
- Spray mist
Physio-chemical and biological processes
Whose results have been very satisfactory as they relate to the decrease of dissolved metals, the increase in pH and decrease of sulfates. A problem on certain occasions is that these processes result insufficient to completely purify acidic water.
As membranes such as granular, can also be an efficient method, however filtration is more complex and costly to implement than other solutions.
Evaporation ponds with spray mist systems are usually combined with a prior stage of neutralization that corrects the pH of the effluent to values between 7 and 8 by adding caustic soda or lime. This method permits the evaporation of large quantities of water, far superior to natural evaporation, with a very small investment.
Such technology atomizes water droplets, separating them into micro particles and elevating them to heights far above 50 meters, which guarantees high efficiency in the evaporation process.
When locating these areas of intense evaporation, one must take into account that the phenomenon of evaporation is closely related to wind (airing). Sprinklers should be situated, whenever possible, in open areas where wind blows unobstructed, thus insuring that there are no undesirable contributions to the environment.
Separation by decantation or coagulation
As we have mentioned before, as important or more so than the chosen treatment technologies, are the preventative measures taken: to prevent and minimize the generation of acidic waters, detect and characterize potential sources of contamination, as well as discharge points, barrier construction or the concentration and isolation of effluents from the environment.
In this regard, some measures have been developed such as storage in flooded underground mines or below sheets of water, in order to prevent oxidation of pyritic material or storage in surface mining voids. Wikipedia: learn more about Acid Mine Drainage (AMD)