Copper fire refining is to remove impurities (such as sulfur, iron, lead, zinc, nickel, arsenic, antimony, tin, bismuth and oxygen) from crude copper at high temperature.

Crude copper produced in a converter contains 98.5%-99.5% copper. The rest are impurities, such as sulfur, oxygen, iron, arsenic, antimony, zinc, tin, lead, bismuth, nickel, cobalt, selenium, tellurium, silver and gold. These impurities exist in copper and have different effect on the properties of copper. Some will reduce the conductivity of copper, such as arsenic, antimony and tin. Some will lead to cracks inside the materials during the thermal processing, such as arsenic, bismuth, lead and sulfur. Some may make the cold-working property poor, such as lead, antimony and bismuth. All in all, the impurities will reduce the use value of copper. Some impurities such as gold and silver are of high value and economic benefits, so they need recovery and utilization. Therefore, in order to meet the requirements of various uses of copper, crude copper needs to be refined.

 

There are two purposes of copper refining. One is to remove the impurities, improve the purity to 99.5%; the other is to separate and recover valuable elements to improve the comprehensive utilization of resources. 

 

There are two refining methods used: 

(1) Crude copper fire refining directly produces 99.5% refined copper. It is only suitable to crude copper containing a low content of gold, silver and impurities. The refined copper produced is only used in less demanding situations for copper purity.

(2) First, crude copper is fire refined to remove some impurities, cast into the anode and then electrolytic refined. This method can produce refined copper with a copper content of over 99.95%. This is the main process of copper production.

 

The fire refining process of crude copper includes oxidation, reduction and casting. At 1150-1200℃, air is pressed into molten copper; Impurities are oxidized and removed; then hydrocarbon materials are added to remove oxygen in the molten copper; finally molten copper is casted. 

Currently, furnaces used for copper fire refining include the reverberatory furnace, rotary refining furnace and tilting refining furnace. 

 

The reverberatory furnace is the traditional fire refining equipment. It is a surface heated hearth furnace. It has simple structure, is easy to operate and can handle both cold materials and hot materials. In addition, due to the volume of reverberatory furnace, the size of the furnace can be large or small. The processing amount can vary from 2t to 400t. It has a strong adaptability. Cold material processing plants and many small plants use the reverberatory furnace to produce anode copper. The drawback is the low operating efficiency, high labor intensity, and poor operating environment.

 

In most plants, stationary reverberatory furnaces are used for refining. The lining is mainly built with magnesia brick, magnesia alumina brick or magnesia chrome brick. The roof is built with non-burn magnesia chrome brick, chrome magnesia brick or direct bonded magnesia chrome brick. Magnesia chrome brick is used in the upper part of the wall, direct bonded magnesia chrome brick and common magnesia chrome brick in the lower part and silica brick in the bottom. 

 

The rotary refining furnace is fire refining equipment developed in 1950s. It is a cylindrical furnace, equipped with 2-4 air ducts, one furnace mouth and one copper outlet. It can rotate for 360 degree. The rotated furnace body is buried under the liquid surface for oxidation and reduction operation. The product is the anode plate. Therefore, it is also known as rotary anode furnace. Compared with the reverberatory furnace, the rotary refining furnace has a high degree of mechanization and automation, small heat loss and good environmental friendliness. However, due to the depth of the bath, the heated area is small and the melting of the materials is slow, so it is not suitable for cold material process, but mainly for handling hot material. 

 

The temperature in the hearth of the furnace is over 1350℃ in the casting process, even up to 1450℃ in the oxidation process. Since the furnace is rotating, there is no fixed slag line in the furnace. Almost 2/3 of the hearth surface is subjected to corrosion by slags and the scouring of molten metal. Therefore, the magnesia chrome bricks used in the lining should have a high Cr2O3 content, even higher in the oxidizing and reducing port and the copper outlet.  Direct bonded magnesia chrome brick or fused rebounded magnesia chrome brick is used in this part. 

 

The tilting refining furnace is invented by Maerz in 1960s. Based on the reverberatory furnace and rotary refining furnace, it combines the strengths of two furnaces. Its hearth is similar to the reverberatory furnace and maintains its large heat exchange area. It is rotatable like the rotary refining furnace. Fixed air outlets are set and air ducts and slag removal operation are removed, which reduces the labor intensity. It is an ideal furnace for both hot materials and cold materials. However, special shape, complex structure and high investment limit its applications.