The Art of Tailings Farming

In the search for sustainable mining practices, one innovative approach is tailings farming. This technique transforms wet tailings, a byproduct of mining operations, into a resource that can be used for tailings stack construction reducing the area required for storage, failure consequences and the requirements for external borrow. A critical factor is evaporation, which controls the time it takes to convert tailings from a slurry to a competent fill. In high evaporation areas like Australia, this process can take as little as 3 to 6 weeks. However, in low evaporation regions such as Canada, it may extend up to 4 years.

What is Tailings Farming?

Tailings farming is a meticulously designed process aimed at maximizing supernatant water runoff and evaporation. This strategy is crucial for converting slurry or thickened tailings into a competent fill, which is capable of compaction. The ultimate goal is to repurpose these tailings into a stable, manageable material that can support sustainable mining operations.

The Four Steps of Tailings Farming

The transformation of tailings through farming involves a series of carefully planned steps:

Step 1: Site Preparation

The initial stage involves preparing the tailings beach, which is divided into cells approximately 150 meters wide, parallel to the dam crest. For flat beaches, a confining dyke made from excavated and bucket-dumped tailings is constructed approximately 100 meters offshore and stands 0.5 meters high. This preparation is crucial for controlling the tailings deposition and facilitating the subsequent farming processes.

Step 2: Managing Slurry Overflow and Initial Drying

Once the slurry starts to overtop the confining dyke, indicating that the cell is full, deposition is halted. The process then waits until desiccation cracks first appear on the surface. At this point, small trenches are excavated in the cell surface using amphibious excavators, allowing for the free runoff of consolidation water. This step is vital for initiating the drying process and preparing the tailings for further treatment.

Step 3: Accelerating Evaporation

To prevent the formation of a crust on the surface, which can impede evaporation, amphibious excavators periodically turn the tailings. This step is essential for accelerating the drying process, ensuring that the tailings become more manageable and closer to becoming a competent fill.

Step 4: Compaction and Final Preparation

After a period of waiting, which can range from a few weeks to several months depending on environmental conditions, the tailings reach a state where they are competent for further processing. At this stage, a swamp dozer and eventually a compactor are deployed to compact the tailings, finalizing their transformation into a sustainable resource.

The Impact of Tailings Farming

Maximising the effect of solar drying reduces the energy needed to lower the water content and improves the strength in the tailings, to the point where it becomes a potentially competent fill material. Because the strength of the tailings is increased, the deposition area can be reduced by increasing the allowable height and steepening external slopes of the tailings impoundment, thereby reducing the impacted area. Using the tailings itself as dam fill reduces the need for external borrow, which again reduces the impacted area. By reducing the water content and increasing the density of the fill the potential consequences of a dam failure are reduced.