Minera Valle Central Operation — 2022 Technical Report

Minera Valle Central recovers copper and molybdenum by reprocessing fresh and historic tailings through a combination of ball milling, conventional and cascade flotation, and selective molybdenum separation.

The Minera Valle Central (MVC) operation recovers copper and molybdenum from two tailings sources: Fresh Tailings delivered from the El Teniente mine and tailings extracted from the historic Colihues deposit. The process begins with size classification followed by ball milling and a series of flotation steps that produce a bulk copper concentrate. This bulk concentrate is then treated in a dedicated molybdenum separation facility to yield separate copper and molybdenum concentrates. Final products are filtered, dried, and bagged for shipment to smelters.

The Fresh Tailings circuit currently processes 130,000 tonnes per day. Slurry enters a primary classification stage, where the feed has a particle size distribution of 80% passing 250–300 microns. Approximately 25% of the cyclone feed material reports to ball mills for further size reduction. The cyclone overflow from the mills (P80=120μ) advances to rougher flotation. The lower grade fine material and oxide copper reporting to the primary cyclone overflow is processed in a scavenger cascade flotation circuit. This static, self-aerating, gravity-assisted process consists of five lines of concrete cascade flotation cells, each 1.80 m x 0.70 m, providing 185 cascades in total. Feed to the cascade circuit includes Fresh Tailings primary cyclone overflow, Colihues tailings primary cyclone overflow, and rougher tailings.

The Colihues tailings are processed in a separate grinding circuit at approximately 35,000 tonnes per day. About 65% of the Colihues cyclone feed material reports to the ball mills for attrition and particle size reduction. The circuit comprises four ball mills (two 16.5' x 18' with 3,250 HP, one 17' x 28' with 3,500 HP, and one 16.5' x 22' with 3,500 HP) using 1.5-inch steel grinding media. Flotation of the Colihues material produces a first cleaner concentrate that reports to three stages of cleaner column cells to generate a final concentrate. A scavenger flotation circuit of six 27 m³ conventional cells processes the column tails, with scavenger tailings returned to the first cleaner circuit.

The final bulk concentrate, containing 30% Cu and 1% Mo, is pumped to the molybdenum separation plant. There, the pulp pH is conditioned to approximately 8.5 using sulphuric acid and a copper depressant reagent. A countercurrent selective flotation process extracts the molybdenum concentrate. This concentrate is then leached with sulphuric acid to lower the phosphorus content remaining from the copper depressant, achieving commercial quality. The final molybdenum concentrate contains 48% Mo and is filtered, dried, and packaged in bulk bags. The final copper concentrate, containing 30% Cu, is filtered to a moisture content of 9% and stored before truck shipment to the Las Ventanas smelter. Final tailings from the cascade flotation circuit are delivered to three 100-meter diameter thickeners. MVC is authorized to discharge up to 175,000 tonnes per day of tailings to the Carén tailings channel.

The report also describes a proposed Cauquenes Plant Expansion designed to process an additional 60,000 tonnes per day of Cauquenes tailings. Under this expansion, Fresh Tailings processing would be adjusted to 115,000 tonnes per day, with the Cauquenes plant handling the remaining feed. The expansion would utilise mills from the existing Colihues circuit, including two 16.5' x 18' mills with 3,250 HP, one 17' x 28' mill with 3,850 HP, one 16.5' x 22' mill with 3,500 HP, and one 14' x 28' mill with 2,500 HP. A new regrind mill with a 2,300 HP motor would reduce rougher concentrate to a P80 of 50μ. The Cauquenes fines fraction would be processed in a conventional flotation circuit in an alkaline environment with NaSH reagent addition. The expanded plant would also include new column flotation stages and additional conventional cells for scavenging.

Critical Data

Overview

Minera Valle Central is a tailings reprocessing operation in Chile that extracts copper and molybdenum from both current mine tailings and a historic tailings deposit. The plant combines conventional grinding and flotation with a unique cascade flotation system to recover values from lower grade fine material. A separate molybdenum plant selectively separates the two metals from a bulk concentrate. The 2014 technical report details both the current operating process and a proposed expansion to treat additional tailings from the Cauquenes deposit.

Key Process Stages

The current operation follows a defined sequence. Fresh Tailings at 130,000 tonnes per day and Colihues tailings at 35,000 tonnes per day are separately classified and ground. The Fresh Tailings primary cyclone overflow, containing lower grade fine material and oxide copper, reports to a cascade flotation circuit. The Colihues material undergoes more extensive grinding, with 65% of cyclone feed reporting to ball mills. Both streams are processed through rougher and cleaner flotation stages. The bulk concentrate proceeds to the molybdenum separation plant, where pH adjustment and selective flotation produce separate copper and molybdenum concentrates. Final tailings are thickened and discharged to the Carén tailings channel.

Additional Interesting Data and Summary

The cascade flotation circuit represents a notable design feature, using static, self-aerating concrete cells arranged in 185 cascades across five lines. This gravity-assisted process treats the lower grade fine material and oxide copper that would otherwise be lost. The proposed Cauquenes expansion would increase total processing capacity, with the new plant incorporating a combination of new and existing equipment. The expansion would reuse mills from the Colihues circuit, including a 14' x 28' mill with 2,500 HP, and add a new regrind mill. The expanded molybdenum plant would handle increased concentrate volumes, with process water recovered from thickener overflow recirculated to the plant.

Key Processes

• Primary classification and ball milling of Fresh Tailings and Colihues tailings
• Cascade scavenger flotation using static, self-aerating concrete cells
• Conventional and column flotation for rougher, cleaner, and scavenger stages
• Selective copper-molybdenum flotation with pH conditioning and copper depressant
• Sulphuric acid leaching of molybdenum concentrate to reduce phosphorus
• Thickening and recirculation of process water from final tailings

Source: 2014 Technical Report , Minera Valle Central Tailings Reprocessing, 2014.

Project website: 2014 Technical Report, Minera Valle Central Tailings Reprocessing