Alfa Laval - Dry Tailings Solutions: Technology Matters

amols blog post02 hero1200x400

Dry Tailings Solutions: Technology Matters

Today, more than ever before, the Mining industry is looking for technical solutions to dewater mine tailings to eliminate the risk of tailings dam failures. But while there is growing industry consensus on the Why and possibly the When, the How is not that straight forward. A vast array of mechnical solutions exist that all promise to deliver dry tailings in a cost-effective way. This leaves miners in the difficult position to navigate the often confusing choices of emerging and established technologies, with engineering teams on sites conducting extensive trials to see what works for their operations.

The key evaluation criteria that mining and mineral processing companies consider while selecting tailings dewatering technologies are:

  • Consistency of dewatered solids – preferably dry, stackable
  • Clarity of filtrate/centrate for recovery and reuse
  • Sound operating economy

What are the Pros and Cons of the most commonly used mechanical technologies available in the market today? Let’s take a closer look at some of the more commonly used products.

Paste Thickener thickens the tailings to a paste-like consistency which is then pumped for mine back-filling or surface paste disposal. In order to achieve this consistency a paste thickener typically has a deep cone design. It needs a fairly large dosage of flocculant and has to be equipped with high-torque drive heads to enable movement of the rake mechanism in the deep bed of solids. Pumping costs are generally high as positive displacement pumps are required for paste discharge. A high degree of supervision is needed to maintain bed depth and underflow consistency. Besides high CAPEX and OPEX, available literature suggests that the output of a paste thickener is difficult to control.

Filter Press incorporates recessed or chamber/recess plates in its design. It uses high filtration pressure to generate a dry solids cake. The filter press gives excellent solids capture when conditioned properly but involves a batch-type operation consisting of several steps. Modern filter press can be equipped with cloth shaking mechanism, automatic cloth washing device, etc, to reduce the manhours in this labour intensive process but are expensive to install. Even with these features, the filter cloth can get clogged due to fine clay particles resulting in prolonged filtration cycles and wear and tear to the filter cloth. Owing to its large footprint and the additional features the modern filter press has a high CAPEX. Changing the filter cloth due to rapid wear and tear and large wash water consumption plus frequent operator intervention lead to a high OPEX.

Belt Press achieves filtration by passing a pair of filtering cloths and belts through a system of rollers wherein the tailings solids are sandwiched between the two filtering cloths. It has low energy requirements and is simple to operate. However, the belt press has a large footprint and requires frequent maintenance and cleaning. Since it has a limited throughput capacity (a 3m x 3m belt press can dewater 20-25 t/h solids on dry basis) the number of units needed for tailings dewatering is high, resulting in high CAPEX. The belt press requires large dosage of flocculant to dewater tailings with fairly high clay content. Large quantities of wash water is required to keep the filtering cloths clean, adding to its OPEX.

Solid Bowl Centrifuge (SBC) consists of a horizontal bowl with a scroll conveyor inside it which is together referred to as the rotating assembly. The assembly spins around its own axis at high speed, thereby generating high centrifugal force that enables separation of tailings solids from the liquid. The separated solids are scrolled out by the conveyor in the form of a dry solids cake whereas the clear liquid (centrate) overflows the weir plates located at the opposite end. Although the SBC technology has existed for several decades it is only in the past 8-10 years that design improvements made by Alfa Laval in wear protection of key components, coupled with changes in its geometry and operating philosophy, have enabled the SBC to be utilized to deliver high solids cake concentration, even at high flow rates. Centrifuge technology requires moderate dosage of flocculant in some tailings dewatering applications but has the highest unit capacity per footprint. As well as having a relatively lower CAPEX, the OPEX is favourable due to its high throughput and lower lifecycle costs.

When comparing options for mechanical dewatering, my advice is to consider the following factors to calculate CAPEX and OPEX correctly:

  • Footprint size, ancillary equipment and installation cost
  • Unit capacity and daily throughput
  • Durability of the material of construction
  • Operating cost including wash water, flocculant, labour, power, compressed air, solids transport, etc.
  • Availability of service support and cost of maintenance (lifecycle cost)

Wherever possible, it is a good idea to carry out pilot tests or lab-scale tests to evaluate the quality of separated solids in terms of its moisture content and stackability as well as solids’ abrasiveness besides checking the filtrate/centrate clarity.

Speak to one of our mining experts

Privacy agreement

That information is stored and processed in accordance to our privacy policy.

Alfa Laval Mining & Mineral Processing Webinars

Curious to learn more? Join the Alfa Laval webinar series discussing challenges and solutions for the mining and minerals processing industry. Equip yourself with the knowledge to design, maintain and manage production processes with high efficiency and minimal operational and environmental risk.

WEBINAR 640X360
.

You might also be interested in

Tailings dewatering - Frequently Asked Questions

What is tailings management?

Many mining and mineral processes require washing the ore to remove impurities. The resulting wastewater and slurries are traditionally stored in tailings storage facilities or TSFs. With depleting ore reserves the quantity of tailings generated is increasing, as miners try to fulfill global demand for minerals. As the practice of wet tailings entails major risks, and new TSF licenses are harder to obtain, the industry is seeking alternatives including tailings dewatering to ensure safe and sustainable tailings management.

How mining companies effectively dewater tailings with solid bowl centrifuge technology

Why is the topic of tailings management receiving so much attention?

Tailings management is in the spotlight as mining companies are balancing growing demand for minerals with slimmer operating margins and greater calls for risk management and sustainability. Shareholder and regulatory pressure as well as social license play a role as well as environmental and cost considerations. The legacy cost of managing and closing a TSF can be substantial.

 

What is the recommended approach for tailings management?

The framework for tailings management considers key development pillars: technological, economic, environmental, policy and social aspects. It incorporates tools for determining trade-offs inherent in different tailings management methods during operation and throughout the life of mine which include Life Cycle Assessment (LCA), Net Present Value (NPV), Decision Analysis, and others.

The design and management of a TSF requires a multi-disciplinary approach as it involves civil and environmental engineering, geology, hydrology, geochemistry, mechanical engineering, process engineering and mine planning.

What are the most cost effective technology solutions available for tailings dewatering?

The key evaluation criteria that mining and mineral processing companies consider while selecting tailings dewatering technologies are:

  • Consistency of dewatered solids – preferably dry, stackable
  • Clarity of filtrate/centrate for recovery and reuse
  • Sound operating economy

Solid bowl centrifuges compare favourably in all three categories.

Can mine operators move away completely from tailings storage with tailings dewatering?

As solid bowl centrifuges have evolved in capacity and throughput, the ranks of mining companies aiming to eliminate TSFs completely with full scale deployments is growing quickly.

For example Australian mining company Bloomfield is moving away from tailings storage with Alfa Laval solid bowl centrifuges. However tailings dewatering can also be an interim solution for sites where tailing dams are reaching capacity. Contact Alfa Laval Australia for more information of our full scale skid mounted SBC solution.

What are the sustainability benefits of tailings dewatering?

Water scarcity brings sustainability to the forefront and water management is also critical for maintaining community support and social license to operate. Considering the arid nature of the Australian continent, it doesn’t come as a surprise that local mining companies are well advanced when it comes to seeking more efficient ways to dewater their tailings and re-use the process water in their processing plant.

Solid bowl centrifuges allow to re-capture up to 90 per cent of the water, as the centrifuge separates the fine solids using G-forces from the contaminated process water. The solids are discharged as a cake with a low moisture content that can be dry-stacked, and used for mine rehabilitation in a similar fashion to overburden and coarse rejects.

Recycle, reuse and recover resources from tailings

Can I dewater slimy tailings with high clay content?

Slimes are sometimes a fraction of the tailings stream, combined with coarser solids, or a product of a desliming stage.  The higher this fraction, the more difficult the tailings are to manage. While filtration can struggle with clay, a gravity-based method such as a thickener commonly separates out the water and solid phases with the assistance of flocculent. They create an overflow that is normally clear enough for use in the process plant, and a pumpable underflow. 

How to dewater tailings slurries with slimes and ultra-fines