FI71952C - Process for the preparation of a mineral rust. - Google Patents

Description

1 71952

This invention relates to improvements in sulfide mineral roasting processes. More specifically, this invention relates to a process for preparing a mineral sulfide roast having a sulfur content of less than about 1%.

The overs roasting of sulphide mineral concentrates, such as sphalerite or chalcopyrite concentrates, in a fluidized bed roasting process offers the possibility of producing calcine containing relatively small amounts of sulfur, for example less than about 1% sulfur. However, experience has shown that the actual sulfur levels in fluidized bed calcined calcines are typically in the order of 2-3 percent. The higher sulfur levels measured in fluidized bed calcined calcines are mainly due to the sulfation of the calcine carried by the hot roasting furnace gases and transported the particulate matter to recovery systems such as cyclones and / or electrostatic precipitators. This sulfation occurs at the lower temperatures in the waste boiler or particulate matter recovery systems by the reaction of a metal oxide in calcine with sulfur trioxide in the gas, as shown in Equation (1) below for copper oxide.

CuO + SO 3 -) CuSO 4 (1)

Sulfur trioxide is formed by the reaction of sulfur dioxide generated during roasting with excess oxygen in the roasting furnace gas (Equation 2).

^ SO2 + 1/2 02 -> SO3 (2) Thus, although the presence of excess oxygen is desirable during roasting to ensure complete removal of sulfur from the mineral concentrate, the presence of excess oxygen in the recovery system is undesirable because it results in the formation of sulfur trioxide, which in turn increases sulfur content of calcine.

2 71952 According to the present invention, there is provided a process for the preparation of metallic calcins having relatively low sulfur contents, for example less than about 1% sulfur. The invention is characterized in that a mineral concentrate having fluidizable particle sizes is provided; fluidizing said mineral concentrate in a fluidized bed reactor with an ascending oxidizing gas, wherein said mineral concentrate is roasted into a metal oxide-containing roast and an exhaust gas containing a metal oxide-containing entrained roast is obtained; and providing a reducing environment above the fluidized concentrate in amounts sufficient to reduce at least a portion of the SO 2 in said exhaust gas to SC 2, thereby preventing at least partially sulfation of the metal oxide entrained in the exhaust gas; and recovering the entrained calcine from said exhaust gas stream to obtain a mineral calcine having a sulfur content of about 1 percent.

In one embodiment of the present invention, the reducing gas is provided above the fluidized bed by feeding a carbonaceous reducing agent such as pulverized coal, natural gas, methane, propane, oil, hydrogen, etc. to the fluidized bed reactor above the fluidized bed concentrate layer.

Referring now to the figure, which is a schematic drawing showing the use of a fluidized bed reactor in the practice of the present invention, there is shown a vertical reactor 10 of the type used for fluidizing and roasting mineral concentrates such as copper, zinc and nickel concentrates. Reactor 10 is provided with a pipe 11 for supplying mineral concentrate to the reactor. It is also provided with a pipe 12 for supplying oxidizing gas for fluidizing and roasting the mineral concentrate. Reactor 10 is provided with a grid 14 which distributes an ascending oxidizing gas which is used to fluidize the particulate mineral concentrate solids above the grid. In the figure, the fluidized bed of mineral concentrate solids is generally indicated by reference numeral 15. As can be seen, the reactor is also provided with a pipe 16 for removing the calcine and a pipe 17 for supplying reducing gas to the reactor 10 above the fluidized bed 15.

3,71952

The effluent from the reactor 10 is passed through a pipe 18 to a gas-solid separator, such as a cyclone 19, where the entrained solids are separated and removed from the exhaust gases. The solids are removed from the cyclone via line 20 and the exhaust gases come out of the top of the cyclone and are passed through line 21 to recover SO 2. Optionally, but preferably, the effluent from reactor 10 is passed through a waste heat boiler (not shown) before being passed to a gas and solid separator 19.

Sulfide-containing mineral concentrates containing metals selected from copper, zinc and nickel are used in the practice of this invention. Typically, these mineral concentrates are obtained by crushing and grinding sulfide ores, which are then processed in a concentrator to produce an enriched, finely divided material consisting primarily of metal sulfides and ferrous sulfides. In the practice of this invention, copper concentrates such as chalcopyrite and bornite concentrates are indeed particularly preferred. Although specific reference is made below to the treatment of copper concentrates, it is to be understood that other mineral concentrates, such as zinc and nickel concentrates, may be used in the practice of this invention. For example, a zinc concentrate called sphalerite can be used in the process of this invention.

Returning now to the practice of this invention, the copper concentrates useful herein generally contain about 20 to 32 percent copper and have fluidizable particle sizes that generally range in diameter from about 10 to 250 microns.

As mentioned above, the copper concentrate is fed through line 11 to reactor 10, where it is fluidized by an ascending oxidizing gas which is fed to reactor 10 via line 12. Thus, the mineral concentrate is initially roasted under oxidizing conditions to oxidize the sulfur, iron and copper present, preferably copper to copper oxide (CuO) and iron hematite (Fe 2 O 2). Generally, roasting is performed at temperatures below the melting point of the minerals to 4 71 952 to prevent the fluidized bed from sticking and wetting; however, the temperature must be high enough to promote the conversion of the copper sulphides and ferrous sulphides present in the ore to their corresponding copper and iron oxides in a reasonably efficient manner. Thus, it is particularly preferred to perform roasting at temperatures generally in the range of about 850-1050 ° C, and preferably in the range of about 900-1000 ° C.

As can be readily appreciated, the oxidizing gas fed to the reactor to fluidize the ore may be oxygen or air; however, because air is more economical, it is an inexpensive material for fluidizing and roasting ore concentrate.

The amount of air used is sufficient to provide the excess oxygen needed to convert the copper and iron sulfides present in the ore to their corresponding oxides. The amount typically used is such that it provides about 1.1 times the stoichiometric amount required to oxidize sulfides to their oxides.

As is easy to assess, it is usually not necessary to add heat to carry out the roasting reaction. However, if the heat of combustion of the concentrate is insufficient to maintain the autogenous roasting reaction at the desired temperature, the combustion air can be preheated to temperatures between about 100-500 ° C. Thus, the feed material, especially the chalcopyrite ore concentrate, is fluidized and roasted in the reactor 10 with an excess of rising oxidizing gas, resulting in the presence of a sulfur trioxide and oxygen exhaust gas stream. However, according to the present invention, a reducing gas such as methane is fed above the fluidized bed 15 to the reactor 10 in sufficient quantities to consume any free oxygen present, continuously running the reaction shown in Equation (3) to the right until the system is substantially free of both oxygen and SO 2.

SO3 -> SO2 + 1/2 02 (3) 5 71952

As mentioned, the reducing gas may be, but is not limited to, methane. Thus, for example, by feeding coal or oil to the reactor above the fluidized bed 15 via a pipe 17, similar results are obtained. The minimum amount of reducing agent required is the sum of A and B, where A is the amount of carbon in carbon monoxide, methane, etc. required to combine with all free oxygen, typical examples of which are the reactions shown in Equations (4) and (5) 02 + 2CO - * 2CO 2 (4) 202 + CH 4 - μ CO 2 + 2 H 2 O (5) and where B is the amount of reducing gas corresponding to that required for direct reduction of SO 2 as indicated by Equation (6).

SO 3 + CO - * SO 2 + CO 2 (6) The concentration of SO 2 in the gas stream before reduction varies with temperature, SO 2 and O 2 concentrations; however, essentially all of SO 2 is converted to SO 2.

An additional reducing agent in the exhaust gas, such as carbon monoxide or hydrogen, reduces the copper oxide in the exhaust stream according to Equation (7) below.

CuO + CO - * Cu + CO2 (7) Thus, some of the copper may end up in the particulate materials recovered from the gas-particle separator 19 in the form of copper metal.

The solids recovered in the separator 19 are removed via line 20 and, if desired, combined with the roast which is removed from reactor 10 via line 16. The calcine can then be processed in standard smelting operations or by hydrometallurgical methods to recover copper from it.

6 71952

Although the present invention has been described in particular detail in connection with copper concentrates, other mineral concentrates may be used, such as those containing mainly zinc or nickel.

It should also be apparent from the foregoing that certain changes and modifications may be made to this invention without departing from the spirit and scope of the invention, and that such modifications and variations are intended to fall within the scope of the appended claims.

Claims (9)

Process for the preparation of roasted mineral having a sulfur content below one percent, characterized in that: a mineral concentrate having fluidizable particle sizes is prepared; said mineral concentrate is fluidized in a fluid bed reactor with ascending oxidizing gas, whereby said minera1 concentrate is roasted to a roasting product containing metal oxide and an exhaust gas is obtained which contains entrained metal oxide-containing roasting product; and a reducing environment is provided above the fluidized concentrate, the amount of which is sufficient to reduce at least a portion of the SO gas contained in the exhaust gas to 3 SO₂ gas, thereby sulfating the at least part of the roasting product carried with the exhaust gas. metal oxide is prevented * and the resulting roasting product is recovered from the exhaust gas stream, whereby roasted mineral having a sulfur content of about 1 percent is obtained. Process according to claim 1, characterized in that said mineral concentrate is fluidized with oxidizing gas and roasted at temperatures varying between about 850-1050 ° C. Method according to claim 2, characterized in that said temperatures vary between about 900-1000 °. Process according to any of the preceding claims, characterized in that said reducing environment is effected by the addition of carbonaceous reducing agent to the fluid bed reactor above the fluid bed.