What Is SX-EW? A Simple Guide to Copper Solvent Extraction and Electrowinning
SX-EW (solvent extraction and electrowinning) is the process that turns low-grade copper ore into 99.99% pure copper cathode without a smelter. It is used at many oxide copper operations across Zambia's Copperbelt and North-Western Province, and throughout the Katanga region of the DRC. This guide explains how SX-EW works in simple terms, what each stage does, which consumables it needs and why it matters to mine profitability.
What Does SX-EW Stand For?
SX-EW is short for Solvent Extraction – Electrowinning. It is a hydrometallurgical process, which means it recovers metal using water-based chemical solutions instead of high-temperature smelting. The process has three main stages:
- Leaching – dissolving copper from the ore with sulphuric acid
- Solvent extraction (SX) – separating and concentrating the copper
- Electrowinning (EW) – plating pure copper onto cathodes using electricity
Stage 1: Leaching
Leaching is the first step. Crushed or run-of-mine ore is placed on heaps, in dumps or in agitated tanks, and dilute sulphuric acid solution is applied. The acid dissolves copper minerals, mainly oxide minerals such as malachite and chrysocolla, into solution as copper sulphate.
The copper-rich solution that drains from the leach is called Pregnant Leach Solution (PLS). A typical PLS contains only a few grams of copper per litre, along with iron, manganese and other impurities. It is too dilute and too impure to send straight to electrowinning, which is why solvent extraction is needed.
Leaching consumes large volumes of sulphuric acid, which is why a reliable acid supply is so important. We explain this further in our article on why sourcing sulphuric acid in Zambia is difficult.
Stage 2: Solvent Extraction (SX)
Solvent extraction is a two-step process that moves copper from the impure PLS into a clean, concentrated solution.
Extraction
The PLS is mixed with an organic phase, which is a copper-selective extractant (reagent) dissolved in a kerosene-type diluent. The extractant picks up copper ions and leaves most impurities behind in the water phase. The two phases are then allowed to separate in large tanks called mixer-settlers.
- The copper-loaded organic moves on to stripping.
- The copper-depleted water phase, called raffinate, is returned to the leach. Because it still contains acid, recycling it reduces fresh acid consumption.
Stripping
The loaded organic is mixed with a strongly acidic solution called lean electrolyte, which returns from electrowinning. The high acid strength forces the copper out of the organic and into the electrolyte. The result is rich (strong) electrolyte, a clean solution with a much higher copper concentration than the PLS.
The stripped organic goes back to extraction to pick up more copper. This continuous loop is the heart of SX.
Stage 3: Electrowinning (EW)
The rich electrolyte is pumped into the tankhouse, which contains rows of electrowinning cells. Each cell holds:
- Anodes – usually lead alloy plates
- Cathodes – usually stainless steel blanks
A direct electric current passes through the electrolyte. Copper ions plate onto the cathodes as pure metallic copper, while oxygen is released at the anodes and acid is regenerated. After several days, the cathodes are lifted out and the copper sheets are stripped off. These sheets are LME Grade A copper cathode, ready for sale.
The electrolyte, now lower in copper and higher in acid (lean electrolyte), returns to the SX stripping stage, completing the circuit.
Key Consumables in an SX-EW Plant
Running an SX-EW operation depends on a steady supply of consumables. Shortages of any of these can cut production:
| Consumable | Where it is used |
|---|---|
| Sulphuric acid (98%) | Leaching and electrolyte make-up |
| Copper extractant reagents | Solvent extraction organic phase |
| Diluent (kerosene-type) | Carrier for the extractant |
| Cobalt sulphate | Added to electrolyte to protect lead anodes |
| Guar or smoothing agents | Improve cathode surface quality |
| Electricity | Electrowinning – a major operating cost |
Why Is SX-EW Popular in Zambia and the DRC?
- It suits oxide ores. The Copperbelt has large oxide deposits that respond well to acid leaching.
- It treats low-grade ore. Material that is uneconomic to concentrate and smelt can still be leached profitably.
- It produces a finished product. Cathode is sold directly, without paying smelting and refining charges.
- Lower capital cost. An SX-EW plant usually costs less to build than a concentrator plus smelter.
- Cleaner emissions. No smelter means no sulphur dioxide emissions from the copper production itself.
Common Problems in SX-EW Operations
- Crud formation: Solid-stabilised emulsions build up at the organic-aqueous interface and cause organic losses.
- Organic entrainment: Organic carried into electrolyte can burn cathodes and cause quality problems.
- Iron and manganese transfer: Impurities moving into the electrolyte reduce current efficiency.
- Acid supply interruptions: Leaching slows and PLS copper grade falls when acid runs short.
- Power outages: Electrowinning stops and cathode quality can suffer during restarts.
Frequently Asked Questions
What is the difference between SX-EW and smelting?
Smelting uses high temperatures to melt copper concentrates, while SX-EW dissolves copper in acid and recovers it with solvent extraction and electricity. SX-EW is mainly used for oxide ores; smelting is used for sulphide concentrates.
What purity does SX-EW copper reach?
Well-run SX-EW plants produce LME Grade A copper cathode of about 99.99% purity.
Why does SX-EW need so much sulphuric acid?
Acid is needed to dissolve copper during leaching and is also consumed by other minerals in the ore, such as carbonates. Acid consumption is one of the biggest operating costs in an SX-EW operation.
Reliable Supply of SX-EW Consumables
G & Y Solutions Limited supplies 98% sulphuric acid and mining reagents to leach and SX-EW operations across Zambia and the DRC. We understand plant operations from the inside, and we help procurement teams keep critical consumables arriving on time and on specification.
📞 Call +260 975 574 784 | 💬 WhatsApp +260 966 807 585 | ✉️ sales@gandysolutions.com
Comments
Post a Comment