JNTU B.Tech III NONFERROUS EXTRACTIVE METALLURGY Previous Question Paper (November/December - 2020 - R16)

Hydrometallurgical extraction of copper is primarily employed for low-grade oxide ores or sulfide ores that are amenable to leaching. The process involves three main stages: leaching, solution purification (solvent extraction), and electrowinning.

The process flow is as follows:

1. Leaching: The crushed and ground ore is treated with a leaching agent, typically dilute sulfuric acid for oxide ores. For sulfide ores, bacterial leaching or pressure oxidation is used to dissolve the copper into a pregnant leach solution (PLS).
2. Solvent Extraction (SX): The PLS contains impurities like iron. It is contacted with an organic extractant (a chelating agent) that selectively binds to copper ions, transferring them from the aqueous phase to the organic phase.
3. Stripping: The copper-loaded organic phase is contacted with a concentrated sulfuric acid solution (strip solution), which reverses the extraction process, transferring the copper back into a clean, concentrated aqueous electrolyte.
4. Electrowinning (EW): The purified electrolyte is fed into electrolytic cells. Using inert anodes (typically lead-alloy) and copper cathodes, an electric current is passed through the solution. Copper ions are reduced and deposited as high-purity metallic copper on the cathode.

The flow sheet sequence is: Ore → Leaching → PLS → Solvent Extraction → Stripping → Purified Electrolyte → Electrowinning → Cathode Copper. The barren organic phase is recycled back to the extraction stage, and the spent electrolyte is returned to the stripping circuit, creating a closed-loop system.

The WORCA process (Worcra) is a continuous smelting and converting process developed for the direct production of copper from concentrates. Unlike traditional batch-wise reverberatory or flash smelting, the WORCA process integrates smelting, converting, and slag cleaning into a single, continuous furnace operation.

The process utilizes a long, stationary, slightly inclined furnace divided into three distinct zones: the smelting zone, the converting zone, and the slag-cleaning zone. The operation proceeds as follows:

1. Smelting Zone: Copper concentrate, flux, and oxygen-enriched air are injected into the smelting zone. Here, the concentrate is rapidly smelted to produce matte and slag.
2. Converting Zone: The molten matte flows by gravity towards the converting zone, moving counter-current to the slag. In this zone, additional oxygen-enriched air is injected into the matte, oxidizing iron and sulfur to produce blister copper.
3. Slag Cleaning Zone: The slag produced in the converting zone flows back towards the smelting zone, passing through the slag-cleaning section. In this area, the slag is contacted with matte or iron-rich material to reduce the copper content in the slag before it is discharged, ensuring high copper recovery.

Key advantages of the WORCA process include:

• Continuous Operation: Eliminates the inefficiencies associated with batch-wise charging and tapping.
• High Thermal Efficiency: The process utilizes the heat generated from the exothermic oxidation of sulfides to sustain the smelting reactions, reducing external fuel requirements.
• Environmental Control: The continuous nature of the process allows for a steady, high-concentration sulfur dioxide gas stream, which is ideal for efficient sulfuric acid production.
• Direct Production: It allows for the direct production of blister copper from concentrate in a single furnace, significantly reducing material handling and processing time.