The core goal of non-ferrous metal refining is to remove impurities (such as sulfur, iron, silicon, heavy metals, etc.) from raw materials, purify metals to industrial grade, battery grade, or electronic grade standards. The refining process for different metals varies depending on their characteristics, but can be divided into three core types: pyrometallurgical refining, hydrometallurgical refining, and electrolytic refining. Some scenarios may also combine special processes such as vacuum refining and regional melting. The following is a detailed classification and process analysis:

1、 Core Refining Process Types

1. Fire refining: Physical chemical separation at high temperatures (applicable to most base metals)

Pyrometallurgical refining is a mainstream primary refining method for metals such as copper, lead, zinc, aluminum, etc., which utilizes the differences in melting point, boiling point, and redox properties between metals and impurities at high temperatures, and achieves separation through high-temperature melting, oxygen blowing, slagging, and other methods. The process is mature and has a large processing capacity.

(1) Basic principles

Oxidation and impurity removal: blowing oxygen (or adding oxidants) into molten metal to preferentially oxidize impurities (such as iron, sulfur, phosphorus) into oxides, which combine with slag making agents (such as limestone, quartz sand) to form slag separation;

Reduction refining: For metals that have undergone excessive oxidation (such as excess Cu ₂ O in molten copper), reducing agents (such as heavy oil, charcoal, hydrogen) are added to reduce them to pure metals;

Distillation separation: By utilizing the boiling point difference between metals and impurities, separation is achieved through high-temperature distillation (such as refining zinc, which has a boiling point of 907 ℃, while impurities such as lead and iron have higher boiling points and can be purified through distillation).

(2) Typical application: pyrometallurgical refining of copper

Converter blowing: Place ice copper (a mixture of Cu ₂ S and FeS) into the converter, blow air to oxidize FeS to generate FeO (which forms slag with the slag forming agent), and further oxidize the remaining Cu ₂ S to crude copper (purity of about 98.5% -99.5%);

Anode furnace refining: Crude copper is added to the anode furnace, oxygen is blown to remove impurities such as iron, sulfur, and lead, and then heavy oil is added to reduce excess Cu ₂ O, ultimately obtaining anode copper (purity ≥ 99.5%) for subsequent electrolytic refining.

(3) Advantages and disadvantages

Advantages: High processing efficiency (with a daily processing capacity of up to 100 tons per furnace), simple process, and adaptability to coarse raw materials such as scrap copper and matte;

Disadvantages: High energy consumption (requiring high temperature above 1000 ℃), easy generation of exhaust gas (such as SO ₂), limited purification accuracy (usually only reaching 99.5% -99.9%).

2. Wet refining: chemical separation in solution (applicable to high-purity metals and complex waste)

Wet refining is a core refining method for new energy metals (lithium, cobalt, nickel) and precious metals (gold, silver), which converts metal raw materials into ionic solutions through acid/alkali dissolution, separates impurities through extraction, precipitation, ion exchange, and other means, and ultimately reduces them to pure metals. It focuses on "high-precision purification".

(1) Basic process

Leaching: Dissolve metal raw materials with acid (sulfuric acid, hydrochloric acid, nitric acid) or alkali (sodium hydroxide) to obtain a solution containing target metal ions (such as leaching waste lithium battery cathode materials with sulfuric acid and hydrogen peroxide to obtain a mixed solution of Co ² ⁺, Ni ² ⁺, and Li ²);

Purification and Separation:

Extraction: Add extractants (such as P204, P507) and use the differences in binding ability between different metal ions and extractants to extract the target metal step by step (such as extracting Co ² ⁺, Ni ² ⁺ first, and then separating Li ⁺);

Precipitation: By adjusting the pH value (such as adding sodium hydroxide and sodium carbonate), impurity ions (such as Fe ³ ⁺ and Al ³ ⁺) are generated and removed through hydroxide/carbonate precipitation;

Ion exchange: using ion exchange resin to adsorb trace impurities in the solution for further purification (such as removing ppm level impurities for electronic grade metals);

Reduction/Crystallization: Pure metals or compounds are obtained by electrolyzing, chemically reducing (such as adding iron powder to replace copper), or crystallizing (such as evaporating lithium solution to crystallize into lithium carbonate) the purified solution.

(2) Typical application: Wet refining of positive electrode materials for lithium batteries

Leaching: The positive electrode powder (LiNiCoMnO ₂) of waste ternary lithium batteries is leached with sulfuric acid to obtain a mixed solution of Li ⁺, Ni ² ⁺, Co ² ⁺, and Mn ² ⁺;

Purification: Adjust the pH to 3-4, precipitate Fe ³ ⁺ and Al ³ ⁺, and then extract Ni ² ⁺, Co ² ⁺, and Mn ² ⁺ step by step with an extractant to obtain a single metal ion solution;

Preparation of products: Metal cobalt (purity ≥ 99.99%) is obtained by electrolysis of Co ² ⁺ solution, and battery grade lithium carbonate (purity ≥ 99.5%) is crystallized by adding sodium carbonate to Li ⁺ solution.

(3) Advantages and disadvantages

Advantages: High purification accuracy (up to 99.99%, meeting battery/electronic grade requirements), low energy consumption, and adaptability to complex waste materials (such as electronic waste and waste batteries);

Disadvantages: complex process, long cycle, high reagent cost, and the need to treat wastewater containing heavy metals.

3. Electrolytic refining: final purification by electrochemical method (suitable for metals with high-precision requirements)

Electrolytic refining is the "final purification stage" after pyrometallurgical/hydrometallurgical refining. Using electrochemical principles, crude metal is used as the anode and pure metal is used as the cathode. By passing electricity, the crude metal on the anode is dissolved, and pure metal is precipitated on the cathode. Impurities remain in the electrolyte or anode mud. It is a key process for achieving high purity of metals such as copper, nickel, gold, and silver.

(1) Basic principles

Anode (crude metal): Oxidation reaction occurs, and crude metal dissolves into ions (such as crude copper anode: Cu -2e ⁻=Cu ² ⁺). Impurities that are more active than the target metal (such as Fe, Zn) will also dissolve into ions, while inactive impurities (such as Au, Ag) will settle into anode mud;

Cathode (pure metal): Reduction reaction occurs, and target metal ions preferentially precipitate (such as pure copper cathode: Cu ² ⁺+2e ⁻=Cu). Active impurity ions (such as Fe ² ⁺, Zn ² ⁺) will not precipitate at the cathode due to low electrode potential;

Electrolyte: carrying metal ions to maintain charge balance in the system (such as copper sulfate+sulfuric acid solution used in copper electrolysis).

(2) Typical application: Electrolytic refining of copper

The anode copper (purity 99.5%) obtained by pyrometallurgical refining is used as the anode, and the pure copper foil is used as the cathode, which is placed in a copper sulfate electrolyte;

Apply direct current (voltage 0.2-0.3V), dissolve the anode copper into Cu ² ⁺, and precipitate pure copper (purity ≥ 99.99%, i.e. "electrolytic copper") at the cathode;

The anode mud is enriched with precious metals such as gold, silver, and platinum, which can be further extracted.

(3) Advantages and disadvantages

Advantages: extremely high purification accuracy (up to 99.99% -99.999%), stable product quality;

Disadvantages: High energy consumption, need to be equipped with electrolyte purification system, only suitable for electrolyzable metals.

2、 Comparison of mainstream refining processes for different metals

Core application scenarios for the final purity of mainstream refining combination processes in metal categories

Copper pyrometallurgical refining (converter+anode furnace)+electrolytic refining ≥ 99.99% for wires, cables, electronic components

Aluminum Bayer process (alumina purification)+Hall Elu electrolysis method ≥ 99.7% (primary aluminum) for building profiles and automotive parts

Lead pyrometallurgical refining (reflection furnace oxidation+reduction)+vacuum distillation ≥ 99.99% for batteries and radiation resistant materials

Zinc wet leaching+electrolytic refining/pyrometallurgical distillation refining ≥ 99.99% galvanized sheet and zinc alloy

Cobalt/nickel (new energy) wet leaching+extraction+electrolytic refining ≥ 99.99% (battery grade) new energy vehicle battery

Gold/silver (precious metals) cyanide leaching+electrolytic refining/chemical reduction+refining ≥ 99.999% jewelry, electronic chips

3、 Special refining process (applicable to ultra-high purity metals)

For ultra-high purity metals (purity ≥ 99.999%, i.e. 5N and above) required in semiconductor, aerospace and other fields, special processes are required:

Vacuum refining: Separation is achieved in a vacuum environment (10 ⁻³ -10 ⁻⁵ Pa) by utilizing the difference in vapor pressure between metals and impurities (such as refining titanium and zirconium);

Regional melting: By moving the heating coil to locally melt the metal, impurities are enriched at one end as the melting zone moves, ultimately obtaining ultra-high purity metals (such as refined silicon and germanium, with a purity of up to 99.9999%);

Gas phase refining: converting metals into gaseous compounds (such as titanium tetrachloride), and then obtaining pure metals through thermal decomposition or reduction (such as the production of sponge titanium).

4、 Core principles of process selection

Metal characteristics: Active metals (aluminum, lithium) prefer wet/electrolytic methods, while inactive metals (copper, silver) prefer pyrometallurgical+electrolytic methods;

Purity requirements: Industrial grade using. wire method, battery/electronic grade requiring wet process+electrolysis;

Raw material types: coarse ore/large waste using fire method, complex waste (electronics, batteries) using wet method;

Cost and environmental protection: The pyrometallurgical process has a large processing capacity but high energy consumption, while the hydrometallurgical process has high precision but requires supporting environmental protection facilities.

The refining process of non-ferrous metals is upgrading towards "low carbonization, high precision, and intelligence", such as introducing clean energy (natural gas, hydrogen) through pyrometallurgy, developing green extractants through hydrometallurgy, and combining electrolysis with AI controlled parameters. In the future, it will further balance efficiency, purity, and environmental requirements.