- The Filtration Society - http://www.filtsoc.org -

Volume 16, Issue 3

NEW FILTRATION PLANT FOR THE STORAGE OF BAUXITE RESIDUES AT AN ALUMINA REFINERY
Lloyd Holliday, R. Medeiros, M. de Castro and V. Hartmann (pages 158-164)

Hydro Alunorte have historically used vacuum drum filters for red mud filtration and Giulini dry stacking technology for residue storage. Studies have been completed and Hydro is now implementing new technology with a new filtration plant that uses fast opening filter presses and a change to dry residue storage. The new system, which is under construction, will increase the solids content of the residues to 78% w/w solids, decrease the caustic content in the residues, increase the recovery of caustic soda for reuse, reduce the ratio of washing water to red mud solids, significantly decrease the land area needed for residue disposal and lower the amount of surface water to be treated. The new technology is considered to be the most sustainable way forward for the industry.

Instead of using an independent engineering company, Hydro decided to draw on the expertise and experience of the filtration equipment supplier for the design and construction of the filtration plant. This paper gives an overview of the most important considerations when designing a filter press plant for red mud. Most important is personnel health and safety in operation and maintenance because the process is abrasive, corrosive, scaling and at high temperature. To achieve high plant availability the filter presses are designed to have less and larger components. The logistics within the plant for the storage and changing of filter cloths for the largest filter plates in the world (2.5 m x 3.5 m) will be important. Plant performance is to be controlled by process optimisers.

PRODUCED WATER TREATMENT: PILOT TEST RESULTS OF AN INTEGRATED MECHANICAL AND MEMBRANE SYSTEM
Arian Edalat and Eric Hoek (pages 164-167)

This paper describes an integrated technology for the treatment of produced water. The results of two field trials are presented in order to demonstrate equipment performance.

DECREASING WATER STRESS, ENVIRONMENTAL HAZARDS, AND POSSIBLE TAILINGS DAM FAILURE
Tuukka Kotiranta, Susanna Horn, Kaj Jansson and Markus Reuter (pages 168-175)

The aim of this study was to improve understanding of sustainability for a ‘minimum impact’ copper concentrator during an estimated 15 years long mine lifetime; background information from earlier studies of minimum impact Cu concentrator operational risk results were used. The operational risks focused on decreasing water stress, environmental hazards, and possible dam break-up. In this paper, the main focus has been set on a conceptual study of simulation and calculation of economics for four different tailings management facility methods and their impact on the site water balance as well as the sustainability assessment.

The selected tailings treatment flowsheets considered in the study are:

• Case 1: conventional (un-thickened)
• Case 2: thickened
• Case 3: paste
• Case 4: filtered tailings options.

All mass balance calculations where performed using Outotec’s HSC Chemistry simulation tool, that provided the basis for the cost calculation. The costs were estimated based on a Finnish cost basis with an assurance of ±30%. The selected location for the concentrator was a flat mine site in a temperate climate zone. Such a scenario showed that the filtered option decreases the water footprint significantly, i.e. from 26.7 to 5.8 kg blue water/kg concentrate produced (or 0.51 to 0.11 kg blue water/kg ore feed) as well as improving the water quality and toxicity indicators.

The simulation results were also used to perform an environmental assessment using the GaBi software. There was no significant carbon footprint and acidification potential variation between the four cases 0.55-0.58 kg CO2-eq/ca. kg blue water/kg concentrate or ca. 0.011 kg CO2-eq/ca. kg blue water/kg ore (when rounded).

LATEST DEVELOPMENTS IN WET CHALLENGE TESTING
Graham Rideal and Abi Stewart (pages 175-180)

There are several important parameters required to unambiguously define pore size in a filter by the challenge test method:

(a) How the pore shape is to be defined
(b) The shape of the challenge particles used
(c) The definition of ‘maximum’ pore
(d) The uncertainty of the measurement.

In addition, the particle sizing instrument used in the analysis must a ‘primary’ method. That is, the results must be traceable back to the International Metre, without any ‘black box’ manipulation.

This paper uses a wide range of woven wire mesh filters from several hundred microns down to a few microns in conjunction with precision glass microspheres to unambiguously characterise the filters. Aqueous suspensions of the filter standards were used as the transport mechanism through the meshes and the penetrating spheres measured by microscopy and image analysis. Provided at least 1000 spherical beads (Maximum size/minimum size <1.2) were analysed, the measurement uncertainty was approximately 3% for both d97 and d99. However, the uncertainty for the d100, Maximum Penetrating Particle (MPP), went up to over 20% and so cannot be recommended as a reliable parameter.