What is hydrometallurgy? A guide to the hydrometallurgy process in mining

Ore grades are in decline. Mineralogy is becoming more complex across deposits. Meanwhile, demand for critical and battery materials is accelerating.

In this challenging environment, mining professionals need a selective, energy-efficient, and environmentally responsible way to extract valuable materials. Hydrometallurgy offers a solution – but to be economically effective, it requires close control.

In this blog, we’ll explain how hydrometallurgy works, lay out the differences between pyrometallurgy and hydrometallurgy, and discuss how on-line analysis provides the rapid insight needed to optimize hydrometallurgy processes.

What is hydrometallurgy?

Hydrometallurgy is a branch of extractive metallurgy that recovers metals using aqueous chemistry. The target metals are dissolved into a solution and then selectively recovered through chemical separation and purification steps.

The result is a highly controllable process that is adaptable to a range of operational parameters, including:

• Ore type
• Feed grade
• Product specifications

The 3 stages of the hydrometallurgy process

There are typically three key phases to the hydrometallurgy process: leaching, solution purification and separation, and final metal recovery.

1. Leaching

The first stage is the dissolution of target metals from solid feed materials using selected lixiviants. Depending on the mineralogy of your ores and the metal you’re targeting, this may involve:

• Acidic systems, such as sulfuric acid
• Alkaline systems, such as carbonate or ammonia systems
• Chloride-based systems

Choosing the right leaching chemistry for your ores is essential, as it directly impacts selectivity, reagent consumption, and downstream processing. Understanding the characteristics of your feed is therefore critical to minimizing cost and maximizing yield.

2. Solution purification and separation

Once the metals are in solution, the leach liquor must be purified and the target metals concentrated before final recovery. Impurities are removed using processes such as:

• Solvent extraction (SX)
  Solvent extraction solutions for hydrometallurgy ensure the selective transfer of metal ions between an aqueous phase and an organic solvent.
• Ion exchange (IX)
  Ion exchange enables the selective adsorption of target ions onto resin.
• Precipitation or cementation
  This is the process of selective removal of metals or impurities through a chemical reaction.

3. Metal recovery

The purified and concentrated solution is turned into a final metal product or saleable intermediate through common recovery routes such as:

• Electrowinning (EW)
  An electric current reduces deposits of high-purity metal onto a cathode.
• Precipitation
  Target metals are solidified into intermediates such as mixed hydroxide precipitate (MHP), mixed sulfide precipitate (MSP), or metal oxide products.
• Crystallization
  A supersaturated solution is created, forcing the target metal to crystallize into a metal salt intermediate such as nickel sulfate hexahydrate.

Hydrometallurgy vs pyrometallurgy: What’s the difference?

The key difference between pyrometallurgy and hydrometallurgy is that pyrometallurgy uses high-temperature processes such as smelting or roasting to separate metals from gangue and impurities. Hydrometallurgy achieves the same result through aqueous chemistry at significantly lower temperatures.

This has practical consequences for energy consumption, emissions, operational flexibility, and more. Pyrometallurgy remains essential for certain commodities, for instance, high-volume materials such as iron and steel.

However, hydrometallurgy has clear advantages for low-grade ores, complex or refractory mineralogy, secondary materials, and operations where selectivity is crucial, for example:

• It offers lower energy consumption compared to pyrometallurgy
• Hydrometallurgy enables high selectivity and process flexibility
• It enables plants to treat low-grade ores, complex mineralogy, tailings, and recycled materials
• Hydrometallurgy generally has a smaller carbon footprint, making it increasingly relevant to mining operations that need to meet strict sustainability targets or regulations

Where hydrometallurgy is used in mining

Hydrometallurgy is applied across a wide range of commodities and processing routes, and the number is growing. The following are the most significant sectors where hydrometallurgy is in regular use.

1. Copper

Heap and agitated leaching of oxide and secondary sulfide ores, followed by solvent extraction and electrowinning (SX-EW), is one of the most established hydrometallurgy processes in the industry.

As ore bodies become more mineralogically complex, with increasing proportions of mixed and transitional ores included in the mix, the importance of flexible, well-monitored hydrometallurgy circuits continues to grow.

2. Zinc

The roast–leach–purification–electrowinning (RLE) flowsheet is the dominant global route for zinc production. Tight impurity control is non-negotiable: elevated levels of iron, copper, cadmium, cobalt, or nickel in the electrolyte directly compromise cathode quality and current efficiency.

Even trace impurities can result in cathode rejection, making precise, continuous monitoring of purification stages operationally critical.

3. Uranium

Uranium processing via acid or alkaline leaching demands precise chemical control at every stage, including in-situ recovery operations, which are becoming increasingly common. Strong regulatory and safety requirements mean that monitoring is essential for risk and compliance management.

4. Rare-earth elements (REEs)

Rare-earth element hydrometallurgy is among the most analytically demanding due to the chemical complexity of the feed materials. Separating individual rare earth elements through solvent extraction or ion exchange circuits is highly sensitive to pH, redox potential, and impurity interactions.

As these materials become more important to clean tech and defence technologies, it is essential for producers to have full insight into their REE processes to control their operations and ensure reliable delivery.

5. Nickel and cobalt

The leaching of nickel laterites, whether through atmospheric or high-pressure acid leach (HPAL) routes, has become an important process in supporting the battery materials supply chain.

Intermediate products such as mixed hydroxide precipitate (MHP) and mixed sulfide precipitate (MSP) must meet strict specifications for downstream refining and battery-grade production.

6. Battery recycling and secondary materials

Hydrometallurgy is frequently used in the recovery of lithium, cobalt, and nickel from black mass: the active material recovered after spent batteries are mechanically processed.

It offers a lower-carbon alternative to pyrometallurgy for lithium-ion battery recycling and enables higher recovery of critical metals at battery-grade purity.

Why monitoring the hydrometallurgy process is critical

Hydrometallurgical circuits are chemically dynamic. Small variations in feed composition, lixiviant strength, or operating conditions can lead to significant changes in performance.

Key variables that continuously change include:

• Metal concentrations in solution
• pH and redox potential
• Acid or lixiviant strength
• Impurity levels
• Phase separation efficiency in SX

Inadequate monitoring in your hydrometallurgy circuit can therefore incur significant risks, including:

• Metal losses to residues or raffinate
• Excessive reagent consumption
• Impurity breakthrough into product streams
• Process instability and unplanned downtime
• Reduced recovery, throughput, and profitability

Effective monitoring is therefore central to process control and optimization and long-term competitiveness – and for the most effective monitoring, industry leaders choose X-ray fluorescence (XRF) technology.

4 reasons to use XRF to monitor your hydrometallurgy process

XRF is a trusted analytical technology in hydrometallurgy, valued for its speed, multi-element capability, and applicability across a wide range of sample types, from solid feed materials and leach residues to process liquids.

The four main reasons XRF is trusted in hydrometallurgy are that it offers:

1. Fast, multi-element analysis
   Operators can simultaneously quantify multiple elements in a single measurement and get results in minutes.
2. High repeatability and precision
   Precision is essential for tight impurity control and metallurgical accounting, helping to prevent rejected batch shipments and costly compliance failures.
3. Minimal sample preparation
   In busy plants, XRF saves time and reduces operator error with its simplicity of operation compared to many wet chemical techniques.
4. Compatibility with a broad range of samples
   XRF can be applied to solids, slurries, and liquids, including via dedicated liquid solutions like the Epsilon Xflow.

Laboratory XRF forms the backbone of hydrometallurgical decision-making. But while laboratory analytics remain essential, relying on lab analysis for process optimization and control can slow down your operations.

Long turnaround times can introduce delays, from 30–60 minutes up to several hours. In fast-moving hydrometallurgy circuits, this lag can mean your plant is operating outside of optimal conditions for extended periods. This has driven growing adoption of on-line and real-time analytical technologies.

How on-line XRF can optimize your hydrometallurgy processes

Real-time elemental monitoring systems such as the Epsilon Xflow enable continuous analysis of process liquids directly in the plant, without the delays associated with laboratory analysis. This enables process optimization through:

• Continuous tracking of metal and impurity concentrations
• Immediate detection of process deviations
• Faster corrective actions and tighter control
• Reduced reagent consumption with more precise dosing
• Improved recovery and product consistency

High-value applications of on-line XRF in hydrometallurgy processes

Real-time analytics shift hydrometallurgy from a reactive operating mode to a proactive, data-driven one. Here are the sectors where it is making the most impact.

Application	How XRF monitoring helps
REE leaching	Helps control dissolution efficiency and manage gangue acid consumption in real time
Uranium leaching	Improves management of uranium concentration, oxidant efficiency, and carbonate or acid balance
Copper SX	Helps monitor organic loading, phase balance, and impurity transfer across extraction and stripping stages
Zinc purification	Facilitates precise, continuous control of impurity removal stages to protect cathode quality
Pregnant leach solution (PLS) management	Ensures stable, on-specification feed to SX-EW circuits

The future of mining depends on effective hydrometallurgy

Hydrometallurgy enables the extraction of valuable metals from increasingly complex resources, but its success depends on precise chemical control.

Advanced analytics, particularly XRF and real-time monitoring solutions such as the Epsilon Xflow, provide the visibility required to optimize leaching, purification, and metal recovery.

Learn more about Malvern Panalytical’s analytical solutions for hydrometallurgy, including the Epsilon Xflow on-line XRF analyzer.