Improving the Bagdad Copper Tailings Thickener with a Reactorwell (TM) Feed System Retrofit
Nestled in the heart of Bagdad, Arizona, lies a copper concentrator with a rich history and a commitment to technological advancement. Originally established in 1942, this facility has undergone numerous expansions and upgrades over the years to meet the ever-growing demands of copper and molybdenum processing. Among its critical components is a Metso High Rate Thickener (HRT), tasked with efficiently handling tailings.
Bagdad copper concentrate plant
Bagdad Concentrator, currently operated by Freeport-McMoRan Inc., is situated near Bagdad, Arizona, USA, and was established in 1942. It underwent several expansion projects in the 70s, 80s, and 90s. After adding a new rougher circuit to the plant in 2013, the total throughput of the concentrator reached around 78000 stpd. At the same time, a 65 m tailings High Rate Thickener (HRT) equipped with a 12 m Vane FeedwellTM was supplied by Metso to thicken the copper tailings slurry from 32% solids (w/w) to +50% solids (w/w) using a flocculant consumption of 30 g/t, before it is deposited into the tailings dam.
The tailings thickener challenges
The ongoing debottlenecking projects in the Bagdad copper concentrator plant in recent years and the upgrade of the primary crusher in 2021 have led to a significant increase in the plant throughput to more than 95,000 stpd. The tailings thickener, originally designed for a throughput of 78,000 stpd, faced challenges due to the increase in solids throughput and feed flow rate, coupled with laundering slurry flow to the feedwell.
The increased feed solids and flow rate disrupted the settling and water clarification processes within the thickener. Excessive flocculant consumption of up to 55 g/t at times was needed due to the high turbulence and shear rate in the feedwell, leading to inefficient flocculation and solids settling. This not only resulted in thickener rake blockages, causing upstream disturbances and necessitating frequent complete shutdowns of operations, but also caused severe bridge vibration. In addition, the existing feed system faced significant issues such as high wear in the feedwell and feed pipe due to high-velocity slurry associated with the laundering slurry flow.
Feed system upgrade with the incorporation of ReactorwellTM
To resolve the issues of the tailings thickener resulting from the increased plant throughput and high feed velocity, a new feed system, including a break tank, twin feed pipes and ReactorwellTM, was designed to replace the old feed system. The break tank guarantees the dissipation of feed slurry kinetic energy and full-bore flow of the feed pipes, ensuring proper feed presentation into the feedwell. The feed slurry is first received in the break tank and then transported to the ReactorwellTM using two fully submerged feed pipes to minimize air entrainment of the slurry and to avoid high-velocity flow associated with laundering flow in the feed pipes. This ensures the feedwell receives effectively de-aerated slurry at the design velocity for optimum performance.
A 13 m ReactorwellTM was chosen for the upgrade project to replace the old 12 m Vane-FeedwellTM. Metso’s ReactorwellTM, depicted in the following figure, is a recent innovation in the feedwell technology. Unlike other feedwell designs in the market, the patented ReactorwellTM features a feed trough connected to the feed pipe, effectively isolating incoming feed from the feedwell environment. This design prevents the transfer of centrifugal momentum and turbulence to the slurry within the ReactorwellTM and dissipates excess feed kinetic energy.
The discharge nozzles and trough in the ReactorwellTM design also help distribute feed slurry evenly and reduce the risk of short-circuiting, common in feedwells with high feed density, low feed flow rates and large particle sizes. The feedwell has auto-dilution ports evenly spaced around the body, at the base level of the trough. These ports allow immediate and efficient dilution of the introduced feed slurry, enhancing flocculation efficiency. A deflector cone, similar to the Vane FeedwellTM, helps manage dilution water flow, maintaining slurry retention time, preventing short-circuiting and restricting uncontrolled dilution flow from below.
To ensure an optimal design and functionality of the ReactorwellTM for the Bagdad tailings thickener, extensive computational fluid dynamics (CFD) simulations were conducted and flow patterns and velocities of the feed slurry were analyzed. The target was to dilute the feed slurry from 34% solids (w/w) to 19% solids (w/w). The CFD results below indicate that the entire Reactorwell™ capacity is utilized during the operation (1). This has helped achieve a high solids hold-up and consequently, a high solids retention time, enabling floccules to mature and develop. Also, the solids are evenly dispersed within the Reactorwell™, creating a favorable environment for uniform and effective flocculation (2).
Furthermore, the simulation results confirm that the symmetrical exit of the material at the discharge of the ReactorwellTM promotes even distribution of floccules throughout the entire thickener, enhancing solid hold-up within the thickener (3). The low shear rate at the exit plate gap minimizes floccule breakage, improving particle settling rates and thickening performance (4). Achieving uniform solids distribution and exit shear rates of less than 200 s-1 in feedwells larger than 9 m in diameter is challenging and very few designs can accomplish this.
Benefits of the feed system upgrade at Bagdad
The new feed system including the ReactorwellTM has yielded remarkable results in resolving the operational challenges. By incorporating the break tank and ReactorwellTM, bridge vibration issues were effectively addressed, ensuring stability even under maximum throughput conditions. Furthermore, the integration of a break tank prevented air entrainment and enabled full-bore flow in the feed pipes, reducing wear and tear significantly.
Post-installation, the performance of the thickener underwent detailed analysis to evaluate the effectiveness of the ReactorwellTM and the overall impact of the feed system upgrade. The results showcased a substantial improvement of 20% in throughput compared to the original design solids loading of 0.97 t/m2h. With the thickener operating at significantly higher solids loading rates, the upgrade alleviated previous limitations and enhanced overall efficiency. Despite fluctuations in process parameters, such as feed particle size distribution and operating conditions, the ReactorwellTM consistently maintained thickening efficiency and underflow density, contributing to process stability.
Moreover, compared to the average flocculant consumption of around 25 g/t pre-upgrade, a significant reduction of around 30% was observed post-upgrade, leading to cost savings and improved process economics.
Despite lowering flocculant dosage, thickener performance remained stable, with underflow solids percentage and overflow turbidity meeting desired specifications. The ReactorwellTM‘s capability to efficiently dilute feed slurry, mix it with flocculant solution and discharge evenly throughout the thickener has facilitated optimal utilization of resources while minimizing operating costs.
To conclude, the integration of Metso’s ReactorwellTM feed system including effective upstream design has significantly improved the performance, addressing previous challenges and enabling higher throughput. The enhancements highlight the ReactorwellTM‘s efficiency in optimizing feed slurry dilution, flocculation, and discharge, ultimately reducing operating costs and enhancing water recovery in mining and mineral processing operations.
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