Engineering & Mining Journal

JUL 2019

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56 E&MJ • JULY 2019 www.e-mj.com PROCESSING SOLUTIONS Vale announced it has invested near- ly R$66 billion (US$ 17.5 billion) in- stalling and expanding the use of dry processing for production at its iron ore operations in Brazil during the last 10 years. It estimates it will spend an addi- tional R$11 billion (US$ 2.5 billion) in similar processing facilities over the next several years. Currently about 60% of Vale's production is from dry processing and the goal is to reach 70%, according to the company. Vale said the "natural moisture" or dry approach for processing is used at its Carajás, Serra Leste and the S11D Eliezer Batista Complex, in Pará, Brazil, and sev- eral plants in Minas Gerais. The main Carajás plant is being converted to dry processing. Eleven of the plant's 17 pro- cessing lines are "dry" and the remaining six wet lines will be converted by 2022. Serra Leste's plants in Curionópolis and S11D in Canaã dos Carajás also do not use water in ore treatment. In S11D, for example, dry processing reduces wa- ter consumption by 93% when compared with conventional iron ore production. In Minas Gerais, the company's use of dry processing increased from 20% in 2016 to 32% in 2018, involving plants at Brucutu, Alegria, Fábrica Nova, Fa- zendão, Abóboras, Mutuca, Pica and Fábrica. The next objective is to imple- ment it at locations in Minas Gerais, such as the Apolo and Capanema proj- ects, which are currently pursuing envi- ronmental licensing. Dry processing is linked to the quality of the iron ore mined. At Carajás, iron content in the ore is high (above 64%), and it only requires crushing and sizing. At Minas Gerais, average content is 40% iron, contained in itabirites. To increase the content, the ore is concentrated by wet processing and resultant slurried tailings are deposited behind dams. In order to reduce the use of dams, Vale plans to invest approximately R$1.5 billion (US$390 million) to implement dry stacking technology in Minas Gerais during 2020-2023. Its goal is to account for up to 70% of the tailings generated in the future, but it noted that success will depend on improvements in technol- ogy as well as on external issues such as environmental licensing. Vale said dry stacking technology doesn't yet exist that can handle its volume of production, particularly in re- gions that experience heavy precipitation levels. In 2011, the company conducted a R$100 million dry-stack pilot project at Cianita in Vargem Grande. The project was completed in 2018 and technicians have been evaluating the geotechnical results. According to the company, its next test of dry-stack methods will be applied on an industrial scale at the Pico mine in Itabirito. Another possible solution, said Vale, is dry magnetic concentration of iron ore, based on technology developed by N Steel, which it acquired late in 2018 for R$1.9 billion (US$500 million). The technology eliminates the need for water in concentration of low-grade ore and produces tailings that are similar in character to those needed for dry stack- ing. The technology, however, is still in the development stage and is not yet ready to be applied on a large scale, ac- cording to the company. BacTech Returns to Stockpile Project With New Partners BacTech Environmental Corp. signed a letter of intent with GMR Inc. to license BacTech's proprietary bioleach technol- ogy as part of an effort to develop a vi- able metallurgical solution to process a "problem" stockpile of arsenic-bearing material at Snow Lake, Manitoba, Can- ada. It also will collaborate with Dundee Sustainable Technologies (DST) as a technology partner in developing a po- tential solution for the problem. The project involves a stockpile of ar- senopyrite concentrate containing resid- ual gold and silver contents. In Decem- ber 2011, BacTech signed a contract with the Mines Branch of the Manitoba Department of Innovation, Energy and Mines to remediate the stockpile. Bac- Tech drilled and assayed the stockpile in 2011 and produced a NI43-101 report. However, as the company's website explained, there were three inherent problems with the Snow Lake project that eventually doomed it. First, the price of gold dropped dramatically, reducing the value of the concentrate going into the bioleach circuit. Second, the iron to arse- nic ratio, which should be 3:1 to make a benign ferric arsenate product, was only 1.8:1 The additional cost of adding fer- ric iron to the process raised the cost per Vale Spends $17.5B on Dry Processing, Plans $2.5B More Dry processing of iron ore, using only the natural moisture contained in the material, is now being used at several of Vale's Brazilian operations, including the S11D Eliezer Batista Complex, pictured above. The company says dry processing has reduced water consumption by 93% at S11D, when compared with conventional processing methods.

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