Every mineral processing operation has some areas that are inefficient and cost them money every day. Understanding where these areas might be and how value losses occur is a fundamental aspect of continual process improvement that needs to be constantly monitored. MinAssist has begun a program of offering targeted health checks for operations to rapidly monitor key areas where cost savings or recovery improvements might be achieved. These are off-the-shelf programs designed to make implementation of process mineralogy as a tool easy and accessible to busy operations personnel.
In developing theses health checks we have been looking at the areas in which operations lose money and thought that this information would be very useful to everyone looking at process improvement. In this post we will explore some key areas where cost savings or recovery improvements can commonly be made. Over the next few weeks we will delve deeper into each of these areas to provide you with an insight into how process mineralogy can help in making measurable improvements in any operation.
In this post we will provide a brief overview of some of the key points in each of these areas. This will be further developed in coming weeks when we will explore each of the key areas in more detail.
Constantly changing material composition in the feed will lead to an ongoing state of change in the mill operating parameters. Any change in feed conditions will affect the grinding conditions and will require changes by the operators in reagent additions for flotation or leaching. However, by the time a variation in material feed has usually been identified and the operators are able to respond a period of time has passed where sub-optimal recovery conditions were present in the process. Even with an experienced team of operators there is an additional period in which changes are made and the process is made stable again. Through this period metal losses occur and generally overcompensation occurs in reagent addition, leading to excess reagent consumption.
Feed variability occurs in every operation, it is in the very nature of mineral deposits. However, when the feed ore type or blend changes multiple times in one day, or even within one shift, significant losses can occur with a direct result on the efficiency of the process. MinAssist has performed audits on a number of operations where poor blending processes and mine planning led to variations in the feed on almost an hourly basis, leaving the process in a constant state of flux. In these situations recovery improvements of up to 10% could be achieved simply by evening out the feed composition, adding significantly to the value of the operation and saving costs through reduced reagent consumption.
In MinAssist’s experience the variability of ore feed to an operation is the primary driver in losing money and is often the catalyst for many of the other areas for losses detailed below.
Comminution processes account for 3-4% of the world’s energy usage and is responsible for at least 40% of energy usage in mining and mineral processing. Inefficient crushing and grinding therefore represents one of the most significant areas that operations lose money. These inefficiencies can be caused by variability in the hardness of the feed material, which may lead to softer material progressing faster through the circuit while harder material spends more time in the circulating load. This can be exacerbated when the feed is variable.
Another key area where inefficient grinding occurs is when throughput is pushed too high to meet production demands. The grinding circuit is often a bottleneck in process throughput and the temptation exists to increase throughput and benefit from the economies of scale. If not properly planned this can result in under-grinding of the material and poor value mineral liberation. This has a flow-on effect resulting in poor recovery or concentrate grades in downstream process circuits. Problems also occur when insufficient throughput is present (I.e. At times of restricted supply from the mine).
MinAssist has already released an off-the-shelf Health Check to provide a simple way to evaluate the status of your grinding circuit. If you are interested you can find more information in our Grinding Optimisation Health Check flyer
Inefficient or poorly maintained cyclones or screens can result in poor classification of material. This in turn can lead to material that has already been sufficiently ground being directed back to the grinding circuit or poorly ground material progressing through the flowsheet when it should be sent back to the grinding circuit. In the first instance overgrinding may occur, which not only expends energy that could otherwise be saved but runs the risk of reducing the particle size distribution of value elements to below the optimum range for recovery. Both of these have a direct cost impact on the operation and could be avoided if sufficient understanding of the classification circuit was maintained.
A direct result of under-grinding is that mineral grains targeted for recovery remain locked within host particles. This means that when those particles enter the flotation or leaching circuit they pass directly through to the tailings stream. In some cases the mineral grain may be partially liberated but attached to a larger gangue particle, which in the case of flotation would require greater reagent addition to recover to the concentrate and when recovery was achieved, dilution of the final concentrate grade.
The use of excess reagents in flotation or leaching is generally a symptom of other issues in the process, however, it is a primary area in which operations lose money. If the feed material is poorly understood and recoveries are not being maintained the natural response of operators is to increase reagent dosage in an attempt to compensate for variations. This leads to reagent addition schemes that are naturally tailored for the worst case conditions, which may only occur rarely, and at all other times excess reagents are present. This is a direct cost to the operation that can be avoided with a better understanding of the material being presented to the circuit, whether it is flotation or leaching.
Every operation needs to target recovery of saleable commodities, however, often the presence of deleterious minerals or elements in a concentrate can result in penalties to the price or in extreme circumstances a concentrate that is un-saleable. Understanding the distribution of these deleterious components is vital for any operation looking to sell concentrate and strategies to minimise their recovery should be put in place
Consideration of the water quality in an operation and effect that it may have on each of the process circuits can have a direct impact on costs. The impact of water quality can range from increased maintenance expenses if saline water is used in a flowsheet not designed for it to detrimental effects on flotation or leaching recovery caused by interaction of ions with reagents. For processes operating a metal extraction circuit the quality of water in Ion Exchange or Solvent Extraction is of significant importance in how efficient the circuit may run and which reagents are most appropriate.
Although make-up water quality is a primary consideration, understanding the water balance and how impurities build up within the circuit is of equal importance. Poorly controlled build-up of impurities can have direct impacts on reagent consumptions or recovery. However, the inadvertent concentration of environmentally detrimental impurities prior to final discharge can have significant environmental impacts, leading to at best increased waste processing costs and at worst an impact on the sites social licence to operate.
While excess reagent addition is a big cost, efficient recovery of those excess reagents can mitigate the impact. In systems such as cyanide leaching for gold, the recovery of cyanide both minimises the required cost of the reagent but also reduces costs associated with waste management where free cyanide is present in tailings dams. In many cases the recovery of reagents is not possible but when it is every effort should be made to ensure that it is undertaken.
The definition of residence time within specific unit operations should be determined by design criteria, however, changes in processing conditions or ore types may mean that optimisation might be possible. Constant monitoring of the optimum residence time can allow increased throughput if residence time can be reduced or increased recovery if it is identified that increased residence time is required.
A simple area in which operations can run less than efficiently is through productivity of their operators. This may be due to inexperience or poor workplace morale but can have significant impacts on process efficiency through lack of monitoring or slow reaction to process changes.
The selection of areas addressed here is simply an overview of the myriad of areas in which operations can lose value, however, they represent a cross section of key problems observed by MinAssist. We don’t expect everyone to agree with these assessments and encourage discussion on points you feel we may have missed. Over the next few weeks we will be exploring each of these areas in more detail and are open to recommendations on what may be included. We encourage you to post your own thoughts in this areas and would relish some active discussion on the topic.
To learn more about using Process Mineralogy to help generate value for your operation please download our Digital Book, “Integrating Mineralogy into Everyday Solutions“