IM 2022 July 22 | Page 30

PASTE & FILTERED TAILINGS

Tailored tailings presses

IM Editorial Director Paul Moore talked to Diemme Filtration about application of its technology to two specific tailings areas – iron ore and bauxite

Back in August 2021 , work began on Alcoa Brasil ’ s Filtro Prensa project at its Poços de Caldas alumina refinery , which is supplied by a captive nearby bauxite mine . It represents an investment of BRL310 million ($ 55 million ) that will completely change the technology for disposing of waste at the operation in Minas Gerais . The works were expected to take 15 months , employing around 500 workers at the peak , and the opening is scheduled this year for November 2022 .

The project required nearly seven years of studies . A new bauxite residue filtration facility will transform how the refinery manages bauxite residue – a byproduct of the alumina refining process that is primarily made up of red mud and coarse sand . The coarse sand fraction ( red sand ) comprises approximately 40 % of residue and approximately 60 % of fine silt fraction ( red mud ). It will generate a dry residue , with only 30 % moisture , equivalent to the natural soil moisture , and directs the water removed to the production process , through a closed circuit , to be reused . The dry waste will be transported in trucks and unloaded in a new waste disposal area , where it will be compacted . This is the third Alcoa unit to implement this technology – the other two were in Australia – and the first in Brazil . The process allows for huge water volume savings as the water can now be recycled in a closed-loop system .
The filter press technology is being supplied by Diemme Filtration based in Lugo , Italy , which is part of Aqseptence Group . Filtro Prensa will use two overhead beam GHT25000P filter presses with customised characteristics for Alcoa ( such as valves , electricals and components ). They have 100 plates each but are expandable to 130 . Diemme also supplied similar filter presses for two of Alcoa ’ s Australian alumina refinery sites which are in Kwinana and Pinjarra , both in Western Australia . Alcoa was the first major alumina producer in Australia to use residue filtration .
Filter press technology has advantages that make it particularly suitable for bauxite residue treatment . Compared to other technologies , filter presses allow drier residue ( with residual moisture lower than 30 % w / w ). As a consequence , the material handling characteristics of the cake obtained by using filter presses Diemme argues are far better than results achieved by alternative methods .
In Brazil , Alcoa has three production units , in Poços de Caldas ( MG ), São Luís ( MA ) and Juruti ( PA ), as well as offices in São Paulo ( SP ), Poços de Caldas ( MG ) and Brasília ( DF ), in addition to a significant shareholding in bauxite miner Mineração Rio do Norte ( MRN ) and in four hydroelectric plants : Machadinho , Barra Grande , Serra do Facão and Estreito .
Diemme Filtration overhead beam GHT25000P filter presses supplied to Alcoa
“ Re-defining what it means to be the most sustainable upstream aluminum company requires a deep commitment to continuously improving our footprint and a relentless pursuit of innovation that will help us progress ,” said John Slaven , Alcoa Executive Vice President and Chief Operations Officer last year . “ By continuing to roll out this bauxite residue filtration technology across more of our refineries , we continue to set new benchmarks in regard to resource management while making progress on goals aligned with our Advance Sustainably strategic priority .”
CMP tackles magnetite tailings
Over in Chile , magnetite iron ore major Compañía Minera del Pacífico ( CMP ) has chosen Diemme Filtration as a partner for the installation of a tailings filtration system at its iron pelletisation plant in the Huasco Valley . Forming part of its focus on sustainability , the dewatering technology will make it possible to store dry cake as waste and at the same time , recycle the water .
The project involves three filter presses of model GHT2500F with membrane plates , capable of treating 6,000 t of solids per day with a minimum residual moisture . The units are equipped with feeding pumps , feeders for material handling , and a double washing system ( rinse and high pressure ).
Compañía Minera del Pacífico , a CAP Group
P4 International Mining SUPPLEMENT | JULY 2022