Running out of time
The Hindustan Zinc Ltd (HZL) location at Zawar in Rajasthan, India, includes four mines: Mochia, Balaria, Zawar Mala and Baroi. Mining takes place underground by long hole open stoping. The extracted ore is then crushed and milled before going through a flotation process to produce zinc and lead concentrates. HZL operates zinc concentrators with combined capacity of about 4 MTPA at Zawar.
The tailings slurry generated during beneficiation contains about 40-45% solids and has traditionally been managed in a conventional wet tailings dam. But, with this reaching its capacity and space on site limited, HZL was looking for an efficient and reliable dewatering concept to allow their Zawar site to continue operating and support the company’s planned expansions. This presented a significant challenge.
With no land available nearby for expanding tailings deposition and the very high cost of constructing a new tailings dam, HZL had to switch to a dry tailings management solution in order to extend the operating life of the existing tailings dam. The limited space on site meant that any new equipment would have to be installed on an existing tailings pond, where the ground conditions were very poor.
In addition, the system had to achieve zero-effluent discharge, as well as reduce fresh water use to the point where no additional fresh water was required to operate the system. Reducing industrial water consumption is a key element of meeting sustainable development goals, particularly in regions of high water stress, such as Rajasthan.
Supporting sustainable mining with MissionZeroSupporting sustainable mining is at the core of what we do. And with many regions of the world now facing water stress, reducing the amount of water used in mining is an integral part of that. Our MissionZero ambition is to offer solutions that support zero water waste by 2030. We are well on the way to achieving this. Our dry-stack tailing solution enables the recovery of up to 95% of process water, as well as solving problems associated with waste water management. Importantly, it is also economically competitive with alternative water management options, such as desalination, even for high tonnages.
Assessing the options
HZL was advised a solution based on horizontal belt filters and large clarifiers. Supported by rigorous test work at our Separation Laboratory in Chennai, however, we were able to show that a dewatering solution combining both sedimentation and filtration would better fit HZL’s requirements.
We were also able to draw on the proven performance and reliability of our filters at other HZL sites across India. The fact that we could offer a one-source solution was another key factor in HZL’s decision.
As a result, HZL opted against the conventional process and chose a solution comprising high-density thickener and E-disc filters for the most efficient dewatering performance with the smallest plant footprint. The contract was awarded on an EPC basis. The challenge was to build a tailing management system over an existing tailing pond; this was made possible by choosing a reliable and expert partner for the rock piling for ground stability improvement. Our novel and modular E-House concept was also introduced for the first time in a large-scale FLSmidth Mining project.
Our patented and proprietary technologies allowed us to offer a solution with the smallest footprint, which was ultimately the most important criteria of this project, as it had to be constructed on top of an existing tailings dam in a location with very low soil bearing capacity.
The full scope of supply included:
- One high-density thickener with P-Duc
- Four E-Disc filters and ancillary equipment
- Dry tailing transfer conveyors and stockpile
- E&I and automation (E-House concept)
- Civil and structural works (including dry rock piling for soil stabilization)
This was the first time that HZL chose E-disc filters for continuous operation at one of their plants. Previous projects were undertaken at paste fill plants, where the filters are only required to operate about 30% - 40% of the time in a year. With E-Disc filters, the high-density thicker operates in a unique closed-loop design, ensuring high water recovery and overflow clarity. Meanwhile, our P-Duc auto-dilution technology for high-density thickeners ensures a 50% turndown target ratio is met – another critical aspect of the project for HZL.
It was a challenging project for both FLSmidth and HZL, but we had confidence in our partnership. FLSmidth shared information across projects and showed a collaborative mindset to handle project issues. Their proactive approach and strategic planning helped commission the project and achieve the required performance.
Advantages of the solution
The final installed system has a capacity of 680 tph. Designed cake moisture was 16% but the system actually achieved moisture of 13-14% during the performance guarantee and has managed levels as low as 10-13%.
In addition to its small footprint, key benefits of the system include:
- Recirculation of >86% of the process water present in tailings
- Safe and stable stacking of tailings cakes in an area of high seismic activity
- 50% reduction of storage footprint
- Faster rehabilitation and restoration of storage site at mine closure
- Ensuring water availability for further expansion of production
Working with FLSmidth was a great experience. The compact size and load of FLSmidth’s equipment, combined with its high throughput, made it possible to install the plant over a tailing pond, which is a first of its kind in India. Despite the challenges, FLSmidth also managed the selection and sizing of equipment very efficiently without compromising the maintenance and operational features.
About Hindustan Zinc Ltd.
- Second largest zinc-lead miner globally and largest in India
- 78% market share in India’s primary zinc industry
- Among the top 10 silver producers globally
- Operations in six locations in Rajasthan and Uttarakhand
- Part of Vedanta, a globally-diversified natural resources company