Copper ore containing arsenic

First, roasting

In order to obtain suitable for further processing copper matte smelting desired ingredients, before melting is sometimes necessary to remove sulfur and volatile impurities (such as arsenic) contained in the concentrate by firing. The calcination is usually carried out in a multi-hearth furnace (as is the case with the El Indio mine), while others are carried out in a boiling furnace (as is the case with the Lepanto smelter). Researchers have conducted extensive research on calcination and found that arsenic removal by volatilization depends mainly on temperature, residence time and the type of atmosphere in the roasting unit. If the air supplied during the oxidation of the sulfide is limited, the volatilization is easy to carry out. Under such conditions, after the temperature reaches 218 ° C, the arsenic is sublimed, and the arsenic trioxide (As ₂ O ₃ ) can be separated from the soot by a filtering device:

As ₂ S ₃ +4 _1/2 O ₂ →As ₂ O ₃ +3SO ₂ (1)

However, in the presence of excess air, arsenic forms arsenic pentoxide (As ₂ O ₅ ) which does not volatilize and is easily melted at 315 ° C:

As ₂ S ₃ +5 _1/2 O ₂ →As ₂ O ₅ +3SO ₂ (2)

This arsenic oxide usually in combination with iron oxide ores together to form iron arsenate:

Fe ₂ O ₃ +As ₂ O ₅ →2FeAsO ₄ (3)

As a result, arsenite is usually oxidized and volatilized to form arsenic trioxide (As ₂ O ₃ ) with limited air supply. Under such conditions, the remainder of the calcined material will be mainly iron oxide-magnetite:

3FeS ₂ +8O ₂ →Fe ₃ O ₄ +6SO ₂ (4)

Second, smelting

The purpose is to smelting copper concentrate or calcine the metal sulphides and gangue separation, melting is generally performed at 1250 deg.] C in the presence of a flux is present. At the time of smelting, the raw material added to the furnace is separated into two layers of liquid - that is, a slag layer formed by gangue and slag-forming material and a layer of matte copper which is composed of metal sulfide.

Since arsenic can be volatilized in the form of oxides, arsenic in the raw material will be partially removed. The matte formed at high temperatures consists of the most stable sulfide. For example, Cu ₂ S and FeS are the most stable sulfides of copper and iron, respectively, which are the main components of matte.

According to the 1986 copper company report, when the Bronze grade is close to 80%, the removal of arsenic will be reversed. According to the analysis, the main reasons are as follows: (1) The presence of metallic copper in high-grade matte copper affects the separation of arsenic; (2) arsenic is easily dissolved in metallic copper. See Table 1 and Figure 1 for the distribution and removal of arsenic during smelting and blowing in five different smelting systems in Chile.

Table 1 Distribution of arsenic in various fire processes (%)

Figure 1 Arsenic removal during smelting and blowing in different processes

It can be seen from the above table that the arsenic removal rates of different copper smelting processes vary greatly. The difference in the arsenic removal process (smelting/blowing) can be explained by the different operating conditions of each smelter. For example, material composition, smelting temperature, blowing speed, oxygen-enriched concentration, smoke composition, product composition and product relative amount are different, resulting in different arsenic removal rates. During the smelting stage, arsenic is mainly removed by volatilization and slagging:

In the reverberatory furnace, arsenic is mainly removed by volatilization and slagging. Since the atmosphere in the reverberatory furnace is a weakly reducing property and the furnace has a large capacity, arsenic is easily removed by calcination. In the P-S converter, more arsenic is removed by roasting and slagging.

In the Teninte and Noranda reaction furnaces, the arsenic removal rate is higher in the volatilization mode, and the arsenic removal rate in the slag formation method is lower. The arsenic removal rate of the P-S converter increases as the amount of blasted air increases, so that the arsenic removal rate is higher when the low grade matte is treated. The Bronze grades of the two reactors are approximately the same (about 70%).

The oxygen-rich concentrations of the Tenient and Noranda reactors were 38% and 33%, respectively. The P-S converter uses non-oxygen-enriched air.

Outokumpu type flash furnace and P-S converter. This type of equipment removes less arsenic by the volatilization route because the furnace atmosphere is highly oxidizing, which is beneficial to the formation of As ₂ O ₅ , so that more arsenic can be removed in the slag. It can be seen that due to the large amount of soot circulation, the removal rate of arsenic in such equipment is low in the Bitiante furnace and the Noranda furnace.

Mitsubishi smelting furnace. During the smelting stage, the distribution of arsenic in slag and soot is significantly different. During the blowing process, the distribution of arsenic in slag, soot and blister copper is approximately the same. By strengthening the oxidation treatment, arsenic in the blister copper can be more transferred to the slag. The oxygen enrichment concentrations in the smelting and blowing operations were 48% and 33%, respectively.