Thickening is one of the most fundamental unit operations in mineral processing and hydrometallurgical flowsheets. At its core, the process involves separating solids from liquid by gravity settling, producing a clarified overflow stream and a concentrated underflow slurry. Despite its apparent simplicity, thickening plays a critical role across most hydrometallurgical circuits and is often intrinsic to overall process efficiency and stability.

In hydrometallurgical applications, thickeners are commonly used to recover water back to the process plant, reducing raw water demand and improve overall water balance. They also form a key component of solid washing circuits, such as counter-current decantation (CCD), where soluble metal ions entrained within the solids are recovered and returned to solution.

In preparation for downstream filtration and density control, thickening serves an equally important purpose: increasing feed solids concentration prior to filtration typically results in smaller filtration plant footprints. In many applications, the inclusion of a properly designed thickener upstream of filtration can significantly reduce overall filtration CAPEX through the benefits of pre-thickening.

When “Simple” Becomes Complex

Although thickening is often viewed as a basic process and is well documented in technical literature, operational challenges continue to arise across the industry. These challenges are frequently linked to critical details being overlooked during design. Common issues include inappropriate selection of sizing criteria without sufficient context, insufficient consideration of feed variability, deviations from the intended operating philosophy, and fluctuations in material characteristics over time.

In practice, thickeners rarely operate under steady-state conditions. Variations in feed solids concentration, particle size distribution, mineralogy, reagent regime, and upstream circuit performance can all materially affect thickener behaviour. If these transient conditions are not adequately considered during design, the result is often compromised performance, loss of availability, and unplanned downtime.

The Importance of Informed Thickener Design

Competent thickener sizing requires a thorough understanding of a wide range of inputs.

These include, but are not limited to:

  • settling behaviour
  • compressive rheology
  • underflow yield stress
  • feed variability
  • flocculant selection and dosage sensitivity
  • realistic operating strategies

Unfortunately, project schedules, budget constraints, or limited sample availability often restrict the extent to which these factors are examined.

When these limitations are not properly managed, the risk is transferred downstream manifesting later as operational bottlenecks, unstable underflow densities, excessive torque, poor clarity, or challenges integrating with downstream filtration or tailings systems. Addressing these issues during operation is invariably more costly than resolving them through informed test work and design upfront.

Technology Supports Performance — It Does Not Create It

The thickener market offers a range of reputable vendors, each with technologies that provide distinct advantages. While these technologies can enhance performance and improve operability, it is important to recognise that no technology can fundamentally change the behaviour of a material. The achievable performance envelope is governed by the inherent characteristics of the slurry.

Laboratory and pilot-scale test work therefore play a critical role in defining realistic performance limits. Well-designed test campaigns allow key parameters to be explored, sensitivities to be understood, and credible design conditions to be established. Supplying accurate, representative data to OEMs enables appropriate technology selection and competent equipment sizing. In most cases, performance observed under ideal laboratory conditions represents the upper bound of what can be achieved in practice. Field performance can be supported and stabilised by good technology but not exceeded.

A Practical, Test-Driven Approach to Thickening

No one understands these realities better than Paterson & Cooke. While the firm is globally recognised for its expertise in slurry pipeline transport, tailings, and backfill systems, thickening has long formed an integral part of these circuits and is therefore a core component of Paterson & Cooke’s solid–liquid separation design capability.

Paterson & Cooke conducts detailed thickening test programmes using a combination of bench-scale and pilot-scale techniques, selected to suit client budgets, timelines, and sample availability. Each testing approach is carefully aligned to the project phase and decision-making requirements, ensuring that meaningful data are generated to support technology selection and equipment sizing.

During studies and detailed design, Paterson & Cooke applies in-house thickener expertise to account for realistic operating and transient conditions, ensuring stable, reliable performance across the full operating envelope.

Find out more about our Laboratory and Test Work services.