Thickener modelling improves efficiency

A 25-year project on thickener modelling that has already delivered huge value for the mineral processing industry has now entered a new phase.

Water is used in processing most minerals to metals, ranging from simply washing away waste solids to leaching of target metals with acidic or basic solutions. Having done this, how are the solid and liquid phases then separated quickly and efficiently?

Gravity thickeners (large tanks) are used widely for this and the addition of flocculants and suspensions assists in producing a clear liquid stream from the top of the tank, as well as a thick sludge of settled solids, which is discharged from the bottom. However, despite their importance and widespread use, thickeners can be erratic and inefficient.

Researchers from CSIRO are advancing the science and modelling of thickeners using mathematical and computational fluid dynamics, with great results. According to an independent assessment, their work has already delivered well over US$500 million in value to end users.

“Thickeners suffer from limited throughput, poor solid-liquid separation, operational difficulties and high consumption of expensive flocculants,” said CSIRO Project Leader Dr Phillip Fawell.

“In tailings applications, for example, they frequently fail to deliver the desired solids concentrations, leading to the waste of water and the need for excessively large tailings disposal dams that can cause environmental issues.”

In response, Dr Fawell and his team are creating the world’s first three-dimensional full thickener model as part of the existing multifaceted AMIRA International project. AMIRA International Ltd is a member-based organisation of minerals companies and suppliers which develops, brokers and facilitates collaborative research projects, through which companies can jointly fund research and jointly share the benefits.

“We are applying the models to systematic studies of different designs and operating conditions (changing solids concentration, volumetric flows, dosages) to establish best performance guidelines,” he says.

“Our team expects to deliver control strategies for dealing with specific issues or performance targets.

“We’re also developing a new test that will give the parameters needed to characterise the settling and consolidation of a flocculated feed for process or control modelling from a series of simple cylinder tests.”

Dr Fawell believes this could end up being a new standard method of all such testing.

The project, or series of projects, which has been running for over 25 years, has been strongly supported by the Australian and international minerals industry with sponsorship funding of over $20 million since inception.

Sponsors benefit from the sharing of key information and technology from each of the projects, including online resources such as a knowledge base, a thickener self-appraisal tool and process models and training presentations.

They can also engage the research team to work on their site-specific problems. This has resulted in significant improvements to the performance of more than 150 thickeners.

“What has impressed me is how CSIRO has been able to pass on to sponsors their broader understanding of how flocculation should be done in gravity thickeners,” said Gray Bailey, program manager from AMIRA International.

“There’s no better feedback than hearing from sponsors who have gone back to their sites, looked at their thickeners and said, ‘Now that makes sense!’”

The Minerals Down Under Flagship of Australia’s national science agency, CSIRO, is one of the largest minerals research groups in the world and has a proven track record of working with industry to deliver innovative solutions. Through targeted research, CSIRO addresses the industry’s challenges, driving sustainability, productivity and innovation for its collaborative partners and clients.

This story first appeared in resourceful: www.csiro.au/resourceful.