Seitz, R, 2016 solid-liquid separation - commentary and references - thickeners

Solid-liquid separation processes including thickeners and filters are a critical component of concentrators, including concentrate and tailings handling and intermediate sections. Awareness of the testing procedures, interpretation of results, weaknesses and issues with procedures is essential. This note focuses on thickeners but many of same concerns are also significant for filtration.

There is much good info within 911 Metallurgist website:

https://www.911metallurgist.com/blog/how-to-size-a-thickener

https://www.911metallurgist.com/blog/concentrate-dewatering-thickening

There is also much available in technical literature; see below with links.

Often we fail to discuss issues or opportunities around the solid-liquid separation sections in concentrators. There are issues around design and operation of these units which mineral processing engineers and operators should be aware of. Does anyone have any comments on:

• Issues with running thickener design tests or factors with significant impact to consider when running tests? Parsapour (2016) (below) discusses this.
• Options for debottlenecking thickeners? Some good options are discussed by Parker (below). Does anyone have any comments on alternatives identified and their application?

• Parsapour, Gh.A., et al., Effect of settling test procedure on sizing thickeners, Separation and Purification Technology 122 (2014) 87–95.

1. Parsapour et al. (2014) discuss the effect of settling test procedures on sizing thickeners. This provides insight into considerations when we are running these tests. Does anyone have any comments on issues they have had running these tests or factors with significant impact to consider when running tests?

The main portion of the water in mineral processing plants is recovered in thickeners. The required cross-sectional area for thickeners is generally calculated using the Coe–Clevenger, and the Talmage–Fitch methods. Over the years, changes which were made in the original settling tests procedure led to inaccurate results owing to floc structure variation especially for the flocculated suspensions. In this study, the effect of flocculation history, defined as the initial solids concentration where the flocs first were formed, on their settling velocity was investigated using batch settling tests. The suspensions used for settling tests were prepared by two different methods to arrive at equal solids fractions. The methods were the conventional procedure of adding solids to a known amount of liquid and decantation. Results of all settling tests (with and without flocculant) on various ores, and coal suspensions showed that the settling velocity of particles in any solids fraction of suspension in the mass settling region could be affected (up to 5-fold) by solids content of the suspension at which flocs were first formed. The decantation method provided lower settling velocity compared to that of the conventional procedure. This was attributed to different flocs structure and size which were indirectly verified by the settling tests. In the case of Interkarbon coal preparation plant, this translated to 27% underestimation of the thickener capacity. It was then concluded that the settling tests performed to determine the required cross-sectional area for thickening should be carried out either on a single sample with the solids concentration of the thickener feed or various concentrations from the feed to the underflow concentrations provided that the samples obtained by decantation of the feed sample.

• Parker, B., Debottlenecking of thickeners in a changing environment, Outotec, 2016.

http://www.outotec.com/globalassets/services/documents/outotec_white_paper_debottlenecking_of_thickeners_in_a_changing_environment.pdf

Parker provides listing/discussion of approaches to debottleneck thickeners in existing plants. The good news is that total replacement is not the only available solution. Some good options discussed here. Does anyone have any comments on these alternatives and their application?

Thickeners are utilized in mineral processing for the purpose of solid-liquid separation (dewatering). Thickeners separate an incoming feed slurry (i.e. water with solid particles of either product or tailings material) into two distinct streams; one consisting of clarified water and the second stream being a slurry concentrated with solids.

Thickeners, like most processing technology utilized in minerals processing, are fixed geometry equipment designed for a specific throughput and duty. During the course of the thickeners’ life cycle, in excess of 20 years, they are commonly called on to perform to new process requirements due to changing mineralogical circumstances, revised plant performance criteria and external changes in the operating environment. In addition, aging equipment requires increased levels of maintenance to prevent unplanned shutdown from occurring.

To meet these changing conditions, the operator has an option to upgrade, or modernize, the thickener to ensure it continues to provide the required outcomes efficiently and sustainably. This white paper will discuss the modernization options available for thickeners.

After a brief introduction to the thickening process we move on to discuss the global external pressures on mine operators to give context to the discussion and elucidate the need for efficient resource use.

Next, we look more specifically at how these external influences impact the operator, then we briefly review the options available to overcome these challenges, and we discuss the owner’s decision process: “Modernize or buy new equipment?”

In assessing the decision to modernize, we consider the elements of an upgrade and the advances in thickening technology that allow operators to meet new challenges.

Finally, we will discuss the process of modernizing a thickener so as to achieve the client’s stated outcomes. This includes identifying the issues, working through an investigation process, testwork, and engineering prior to the delivery and implementation of the modernization.

Coe, H.S. and Clevenger, G.H., Methods for determining the capacities of slime settling tanks, Trans. AIME, vol. 55, 1916, 356-384.

http://library.aimehq.org/library/books/Bulletin%20of%20the%20AIME%201916%20-%20109-112/Bulletin%20of%20the%20AIME%201916%20-%20109-112%20-%20082.pdf

Behrouzi, K., et al., Water Recycling at Processing Plants in Water Scarce Regions – a Case Study of Thickener Design for the Mansour Abad Processing Plant, Proceedings Tailings and Mine Waste 2011, Vancouver, BC, November 6 to 9, 2011.

http://www.infomine.com/library/publications/docs/Behrouzi2011.pdf

Dahlstrom, D.a., et al., Liquid-Solid Operations and Equipment,

http://ftp.feq.ufu.br/Luis_Claudio/Books/E-Books/Perry/Chap18.pdf

Garmsiri, H. et al., A new approach to define batch settling curves for analyzing the sedimentation characteristics, JME - Journal of Mining & Environment, Vol.3, No.2, 2012, 103-111.

http://jme.shahroodut.ac.ir/article_88_645e64cf814a980e3c9b7d37234cee26.pdf

Garrido, P., et al., Progress made in pilot and laboratory thickening study, Copper 2013.

http://www.ci-jri.cl/Download/Publicaciones/Copper%202013%20-%20Progress%20made%20in%20pilot%20and%20laboratory%20thickening%20study.pdf

Keane, J.M., Laboratory testing for design of thickener circuit, Concentration and Dewatering Circuits, SME, 498-505.

https://www.911metallurgist.com/wp-content/uploads/2016/09/LABORATORY-TESTING-FOR-DESIGN-OF-THICKENER-CIRCUIT.pdf