Why Process Water Quality is Important in Mineral Processing Plant Operation?
There is no question that water is vital in all aspects of our daily life. That same vital water is also consumed and reused in most mineral processing plants. However, the quality of reclaimed water can sometimes adversely affect the plant operation, and to an even greater extent if the reclaimed water is mixed with the waste water from the mine containing elevated ionic species or organic matter. It is easy to test the quality of primary water quality with today’s technology; however, it typically takes several years of operation to identify reclaim water quality issues before even taking any necessary steps.
If we look at the reclaimed process water alone, the first question may be: ‘what can go wrong after years of operation?’ Basically, experience shows that three types of materials can accumulate to critical levels: 1) total suspended solids 2) the residue reagents used in flotation, thickening and filtration and 3) the dissolved metal ions in process water.
Are these materials really bad for mill operation? The short answer is yes. Depending on where the processed water being reused; the impact on the operation can be significantly negative. Below is a graph showing a simplified gold absorption rate on the activated carbon with plant water from one gold leaching circuit as compared with another using tap water. When using plant water (reclaimed water), the carbon gold loading capacity was reduced significantly which explains why high operating costs were occurred in operation even with carbon reactivation.
Sometimes site operations must involve the use of multiple reagents and with mine water as the fresh water source. Flotation recovery can drop significantly when these two factors are combined. A two-digit recovery decrease can be observed in operations because of that.
You may be wondering how you can solve this problem. Here are some thoughts and recommendations. The first one is to know your water by setting up a water quality monitoring program to manage water mass balance including the water quality data of all the water sources that will be used on site. (e.g. fresh water, mine water and reclaim water etc.) You may also want to ask water quality related questions when you need to use mine water in the mill. Sometimes, although the mine water may contain elevated metals, that does not necessarily translate into a negative impact on mill performance.
Secondly, you need to know your plant circuit and what is being or will be added in. For a green-field project, it is recommended to take cautious steps during the design stages. For example, selecting a more efficient flotation reagent to reduce reagent schedule complexity by working with metallurgists, labs, and reagent suppliers. In operating plants, over-dosing should always be avoided. If the plant is designed to produce multiple products with more than one wet process, consider adding metallurgical testwork by using aged water samples during the design. This can help predict some potential water issues but the impacts sometimes might be underestimated due to the lab scale versus operating scale. Use of representative water samples is critical to get a better view. If this is not possible, try to get some data from a similar operation.
The last point is to know the mineralogical variability of the plant feed materials. This is important for mills with varied mineralogical feed materials.
Please feel free to send your request about water issues in your operation/design work. We are more than happy to hear from you and to be able to help.