Feasibility of Recycling Bayer Process Red Mud for the Safety Backfill Mining of Layered Soft Bauxite under Coal Seams

The mining of layered soft bauxite under coal seams (BCS) will cause serious underground goaf disasters and surface Bayer process red mud (BRM) pollution. In order to realize the safe and efficient mining of BCS, the feasibility of recycling BRM as a backfilling aggregate was explored. A series of tests were conducted to prevent the pollution diversion of BRM from surface storage to underground goafs, and a numerical simulation analysis of the backfilling mining process was carried out based on FLAC3D to protect the overlying coal seam. The results show that: under the action of encapsulation, solidification and inhibiting precipitation from cementitious materials, the leaching concentration of harmful substances in red mud-based cemented backfill (RCB) can be reduced 70% more than fresh BRM. Mining disturbance redistributes the in-situ stress field of overlying strata; normal backfilling can not only reduce the pressure stress of pillars, but also release the tensile stress in the roof and floor from +0.4956 MPa to −0.1992 MPa, effectively preventing roof subsidence. Since the creep damage process of past backfill will absorb and dissipate lots of energy, the disturbance range caused by backfill mining is controlled within 3 m, which is only 10% of the open-stope method.

Influence of lime (CaO) on low temperature leaching of some types of bauxite from Guinea

In Bayer process, low temperature treatment of bauxite generally applicable to gibbsite in the presence of a significant amount of boehmite (>3%), requires a temperature increase and the addition of an additive to improve the leaching conditions. This research is based on improvement of low temperature leaching conditions 108 °C and the addition of lime during the attack of some types of bauxite in Guinea. TRUhat is Low Mono Grade Bauxite (LMG), Standard Metal Grade (SMG) and Fria Bauxite (BF). The results of this study confirm an improvement in the extraction yields. Additionally, it shows an increase in yields of two points when the lime dosage is low, and between 0.5 and 3% of the bauxite weight. Based on the mineralogical and chemical composition findings, minerals contain of SMG bauxites are difficult to decompose while BF bauxites are easy to process. Sougueta limestone was used for testing. After calcination, we obtained CaO added at a rate of: 0.3; 0.5; 1; 3 and 6% of the bauxite weight to finally obtain the highest leaching efficiency compared to the leaching efficiency of bauxite without addition. The best leaching rate obtained for LMG, SMG and BF are respectively: 89.01, 87.15 and 89.74% for additions of 1, 0.5 and 3% CaO respectively.