Waste

SDG 12: Sustainable consumption and production

Target 12.5: Substantially reduce waste generation through prevention, reduction, recycling

Tailings dams pose a high risk because of the semi-fluid nature of the tailings mixture. Stored in slurry form, tailings dams experience tremendous pressure and should the walls breach, the stored tailings are propelled quickly due to the viscosity of the fluid and the release of the stored potential energy.

Tailings slurry contains about 50-55% water. One solution to increase the stability and life of the tailing dam is to de-water the tailings mixture. Hindustan Zinc Limited (HZL) has commissioned a tailing filtration (dry tailing plant) near the tailing dam at Zawar. The installation and commissioning of dry tailing plant has resulted in higher water recovery, near elimination of water losses through seepage and evaporation, virtual stoppage of any probability of ground water contamination through seepage and significant reduction in the risk of catastrophic dam failure. Excess water is extracted from tailing slurry by a filtration process, which transforms it into a cake containing only 16% moisture. The cake is easy to handle, can be transported by conveyor & dumpers, stored in stacks up to reasonable height and stabilized by compaction & plantation. The extracted water is re-circulated for use in the milling operation – thereby reducing our need for withdrawal of fresh water. The dry tailing plant uses multiple stages to dry the tailings. In the “tailings thickener” stage, trash and feed slurry are separated and process water is transferred to a thickener overflow tank. The separated “underflow slurry” is further dried by the addition of a flocculant, to separate the water using a gravity separation system. This increases the slurry composition from 50% to 70%. The water collected in the thickener overflow tank is transferred to different parts of the plant, such as process water pond, flocculent dosing system, firefighting system, and slurry flushing line. A portion of thickener overflow water is transferred to water treatment system through water pumps, where it gets treated and used in the tailing filtration & disposal system. Thickened slurry is sent to the filter feed tank where it is pumped using centrifugal pumps for uniform distribution over the entire width of the E-disc filter.

Key Advantages:

• Recirculation of >90% of the process water.
• Elimination of the risks of catastrophic tailings flow when a slurry dam (TSF) fails.
• Safe stacking of tailings cakes even in areas of high seismic activity.
• Reduction of risk of ground water contamination through seepage.
• Reduction of storage footprint by 50% and enabling fast rehabilitation when approaching mine closure

SDG 9: Industry, innovation and infrastructure

TARGET 9.2: Promote inclusive and sustainable industrialization

Vedanta Lanjigarh Limited(VLL), has a capacity of 2 MTPA metallurgical grade alumina production from its world-class facility at Kalahandi district, Odisha, since 2009. The refinery feeds Vedanta’s Aluminium smelters at Jharsuguda in Odisha and BALCO in Korba, Chhattisgarh. VLL produces approximately 3.0 MTPA of red mud (Bauxite Residue) which is extremely rich in iron oxide and alumina. The residual caustic makes disposal of red mud tough, with limited option to stock it in storage facilities. The storage facility needs to be designed to ensure no environmental contamination, which however are not a permanent solution to the increasing quantity with increased production.

In order to ensure responsible utilization of the residue, we undertook studies to further examine the properties of red mud and find alternate modes of utilization. Red mud being rich in additional material after alumina extraction, has a high potential to be utilized in the clinkers in the cement manufacturing industry as a replace for laterite. Also, the residual caustic, which actually made disposal tough, is useful in controlling the emission of sulphur during the cement manufacturing process. The primary substance used in cement manufacturing is limestone which is used in combination with laterite and red mud is a very effective replacement during this process.