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The HORIZON2020 project "ENSUREAL" is developing a modernized version of the Pedersen process for production of alumina. The process counters challenges in raw material availability, energy availability, CO2 emissions and sustainability. European universities, institutes, technology partners, metal producers, fertilizers and plant suppliers cooperate to consider newest technologies, research results and current boundary conditions like climate change discussions. After calculations, simulations lab tests and pilot tests now all data are evaluated for upscaling to the investigated case, a capacity of 500 kt industrial grade alumina. The flowsheet and the industrial scale plant will be shown as a first complete process concept, consisting of four main sections: Pretreatment, pyrometallurgical melting, hydrometallurgical steps and calcination. The pretreatment contains mixing, milling and pelletizing of bauxite or bauxite residual, limestone, coke and gray mud reverts. In the pyrometallurgical section the pellets are dried, pre-reduced and preheated by a rotary kiln. The hot pellets are afterwards hot transferred to a large SAF to produce a Ca-Al-slag and to separate iron. The Ca-AL-slag is cooled down slowly. This is important to enable the formation of leachable crystal phases and the formation of phases that make the slag self-disintegrating. The modern SAF enables to use renewable enerygy, to integrate energy management and heat recovery. The hydrometallurgical part contains as first step the leaching of the Ca-Al-slag using a recycled Na2CO3 solution, forming solid gray mud (CaCO3) and dissolved NaAlO2. Afterwards the NaAlO2 solution is treated with CO2. As a result dissolved Na2CO3 and solid Al(OH)3 are generated. While the Na2CO3 solution is returned to leaching step the generated Al(OH)3 is finally transferred to the calcination step. The updated Pedersen process requires a long well cooperating process line, gives flexibility in usage of a wide range of raw materials and renewable energy and a contribution to reduce CO2 emissions. |
