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Transforming bauxite residue into soil

Abstract : The annual production of red mud, a by-product from the Bayer process of alumina production, is estimated at 120 Mt. Red mud deposit could be bioremediated (Grafe and Klauber 2011). A low cost and sustainable in situ remediation method for transformation of bauxite residue into soil is designed and tested. A protocol for desalting and amendment of modified bauxite residue to allow the growth of common plants is presented in this paper. The red mud is thickened and washed in press filter, to remove 14/15 of the soda content, and renders it as a wet solid, called Bauxaline at Alteo factory of Gardanne, France. Gypsum is then added to lower the pH from 10.5 to 8.5 (L/S 10 l/kg), and the product is called Modified Bauxite Residue (MBR). Preliminary laboratory tests have shown that the limiting factors for plant germination and growth are salinity and dystrophy (lack of nutrients). Plant growth is limited by the Na2SO4.10H2O salt resulting from the reaction of gypsum CaSO4.2H2O with NaOH, NaHCO3 and Na2CO3 of Bauxaline®. The salt must be removed by drainage. Without evaporation, a net drain volume of 1 l/kg MBR is sufficient. In the presence of evaporation (RBM without vegetation) or evapotranspiration (vegetated RBM), a net drainage volume between 1.5 l/kg and 2.25 l/kg in the surface layer is needed. Gypsum helps to remove Na+ from the exchange sites and flocculates the bauxite residue, resulting in an improved stable structure and an increased hydraulic conductivity. Different compost and fertilizer rate were tested (Figure 1), ending up in a protocol. After the drainage of salts, compost (10 g/kg) and fertilizer (0.7 g/kg of a formula 10-6-10), topsoil for bacterial inoculum (1 g/kg) and grass and legume seeds are added. Watering is necessary in the first year in dry season. Fertilization should be repeated for two years in accordance with agronomic recommendations. This protocol was tested in pots, lysimeters (Figure 2), and field plots at the Alteo company (40 m2)...
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Submitted on : Tuesday, August 7, 2018 - 9:16:31 AM
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  • HAL Id : ineris-01854702, version 1

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Pierre Hennebert, C. Chen, Fadaank Said Ali Mohamed, Laurent Poizat. Transforming bauxite residue into soil. 5. International conference on industrial and hazardous waste management (CRETE 2016), Sep 2016, Chania, Greece. ⟨ineris-01854702⟩

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