Note: Descriptions are shown in the official language in which they were submitted.
~00074
.
-- 1 --
1 This invention is concerned with improvements in
2 sulfide mineral roasting processes. More particularly,
3 the instant invention is concerned with the fluid bed dead
4 roasting of sulfide mineral concentrates, particularly
chalcopyrite and sphalerite concentrates.
6 The dead roasting of sulfide mineral concen-
7 trates, such as sphalerite or chalcopyrite concentrates in
~ a fluid bed roasting process, offers the potential of
g producing a calcine which contains relatively low amounts
of sulfur, for example, less than about 1 percent sulfur.
11 Experience has shown, however, that the actual sulfur
12 levels in fluid bed roasted calcines are typically of the
13 order of 2 to 3 percent. The higher levels of sulfur
14 measured in fluid bed roasted calcines are due primarily
to the sulfation of the calcine entrained in the hot
16 roaster gases and carried over into the particulate
17 recovery systems, such as the cyclones and/or electro-
18 static precipitators. This sulfation occurs at the
19 lower temperatures present in the waste heat boiler or
the particulate recovery systems by the reaction of metal
21 oxide in the calcine with sulfur trioxide in the gas such
22 as is shown in equation (1) below in connection with
23 copper oxide.
24 CuO + S03 ~ Cu~04 (1)
.
The sulfur trioxide is generated by the reaction
26 of sulfur dioxide generated during the roasting with
27 excess oxygen present in the roaster gas (equation 2).
28 S02 + 1/2 2 ~ so3 (2)
29 Thus, althouyh excess oxygen is desirable during roasting
to ensure complete elimination of the sulfur from the
31 mineral concentrate, the presence of excess oxygen in the
2 recovery system is undesirable because it results in the
33 generation of sulfur trioxide, which in turn increases the
34 sulfur content of the calcine.
.1~000~
-- 2
1 In accordance with the present invention, a
2 process for preparing metal calcines having relatively low
3 sulfur contents, for example, sulfur contents below about
4 1 percent, is provided. Simply stated, the present
invention contemplates fluidizing mineral concentrates,
6 especially mineral concentrates containing metals selected
7 from copper, zinc and nickel, in an ascending oxidizing
8 gas, said gas containing sufficient oxygen or other
g oxidizing agent to ensure substantially complete oxidation
of the mineral concentrate while providing a reducing
11 environment above the fluid bed so that the total amount
12 of SO3 present is effectively reduced thereby preventing
13 recombination of sulfur with the calcined concentrate.
14 In one embodiment of the present invention, the
reducing gas is provided over the fluid bed by introduc-
16 tion of a carbonaceous reductant, such as pulverized coal,
17 natural gas, methane, propane, oil, hydrogen and the like
18 in the fluid bed reactor above the bed of fluidized
19 mineral concentrate.
Referring now to the Figure which is a schematic
21 diagram illustrating the use of a fluid bed reactor in the
22 practice of the present invention, there is shown a
23 vertical reactor 10 of the type employed in fluidizing
24 and roasting mineral concentrates such as copper, zinc and
nickel concentrates. The reactor 10 is provided with a
26 conduit 11 for the introduction of mineral concentrate
27 into the reactor. Also, a conduit 12 is provided for
28 the introduct.ion of an oxidizing gas for fluidizing and
29 roasting the mineral concentrate. The reactor 10 is
equipped with a grid 14 that distributes the ascending
31 oxidizing gas used to fluidize the particulate mineral
32 concentrate~ solids above the grid. In the Figure, the
33 fluidized bed of mineral concentrate solids is shown
34 generally as reference numeral 15. As can be seen, the
reactor is also provided with a conduit 16 for removal
36 of the roasted calcine and a conduit 17 for providing a
37 reducing gas in reactor 10 above the fluid bed 15.
38 The effluent from reactor 10 is passed by a
~.~
. .
lZOO~
-- 3 --
1 conduit 18 to a gas-solid separator, such as a cyclone
2 19 in which entrained solids are separated and removed
3 from the offgases. The solids are removed from the
4 cyclone via line 20, and the offgases exit from the top of
the cyclone and are sent via line 21 for SO2 recovery.
6 Optionally, but preferably, the effluent from reactor 10
7 is passed through a waste heat boiler (not shown) prior to
8 being passed to the gas solid separator 19.
g In the practice of the present invention,
sulfide containing mineral concentrates are employed
11 containing metals selected from copper, zinc and nickel.
12 Typically, these mineral concentrates are obtained by
13 crushing and grinding sulfide ores which are subsequently
14 processed in a concentration mill to produce a concen-
lS trated, finely divided material composed principally of
16 metal sulfides and iron sulfides. Indeed, in the practice
17 of the present invention, copper concentrates such as
1~ chalcopyrite and bornite concentrates are particularly
19 preferred. Although particular reference is made herein-
after to processing of copper concentrates, it should be
21 understood that other mineral concentrates such as zinc
22 and nickel concentrates may be employed in the practice of
23 the present invention. For example, the zinc concentrate
24 sphalerite ~nay be employed in the process of the present
invention.
26 Returning now to the practice of the present
27 invention in general, copper concentrates, useful herein,
28 will contain from about 20 to about 32 percent copper,
29 and they will have fluidizable particle sizes ranging
generally froln about 10 ~m to 250 ~m in diameter.
31 ~s indicated above, the copper concentrate
32 is fed into reactor 10 via line 11 where it is fluidized
33 by the ascending oxidizing gas fed into reactor 10 via
34 line 12. Thus, the mineral concentrate is first roasted
under oxidizing conditions to oxidize the sulfur, iron and
36 copper present, the copper preferably to cupric oxide
37 (CuO) and the iron to hematite (Fe2o3). In general,
38 roasting is carried out at temperatures below the melting
12Q()0~7~
-- 4
1 point of the minerals in order to prevent the sticking and
2 bogging of the fluid bed; however, the temperature must
3 be sufficiently high to promote the conversion of the
4 copper sulfides and iron sulfides present in the ore to
their respective copper and iron oxides in a reasonably
6 efficient manner. Thus, it is particularly preferred to
7 conduct the roasting at temperatures generally in the
8 range of about 850C to about 1050C, and preferably
9 in the range of about 900C to about 1000C.
~s can be readily appreciated, the oxidizing gas
11 introduced into the reactor to fluidize the ore can be
12 oxygen or air; however, since air is more economical, it
13 is the preferred material for fluidizing and roasting the
14 ore concentrate.
The amount of air that is employed is sufficient
16 to provide an excess of oxygen necessary to convert the
17 copper and iron sulfides present in the ore to their
18 respective oxides. Typically, the amount employed is such
19 as to provide about 1.1 times the stoichiometric amount
required for the oxidization of the sulfides to their
21 oxides.
22 As is readily appreciated, it is not generally
23 necessary to add heat to carry out the roasting reaction.
24 However, if the heat of combustion of the concentrate is
insufficient to sustain an autogenous roasting reaction
26 at the desired temperature, the combustion air may be
27 preheated to temperatures in the range from about 100C
28 to about 500'~C. Thus, the feed material, especially
29 chalcopyrite ore concentrate, is fluidized and roasted
in reactor 10 by an excess of ascending oxidizing gas
31 thereby resulting in the presence of sulfur trioxide and
32 oxygen effluent gas stream. In accordance with the
33 present invention, however, a reducing gas such as methane
34 is introduced above the fluid bed 15 in reactor 10
in quantities sufficient to consume all free oxygen
36 present, thereby continuously driving the reaction shown
37 in equation (3) to the right until the system is substan-
38 tially free of both oxygen and SO3.
.
1200074
- 5
1 S03 ~ SO2 + 1/2 2 (3)
2 As indicated, the reducing gas may be, but is
3 not restricted to, methane. Thus, for example, introduc-
4 tion of coal or oil into the reactor above the fluid bed
15 via line 17 will achieve similar results. The minimum
6 amount of reducing agent required is the sum of quantities
7 A and B,
8 where ~ is the amount of carbon, as carbon
g monoxide, methane or the like, necessary to combine with
all free oxygen as typified by the reactions shown in
11 equations (4) and (5); and
12 2 + 2 CO -~2CO2 (4)
13 2 2 + CH4 > C2 + 2 H2O (5)
14 where B is an amount of reducing gas equivalent
to that required for the direct reduction of SO3 as
16 shown in equation (~).
17 SO3 + CO ` S02 ~ C2 (6)
.
18 The concentration of SO3 in the gas stream
19 prior to reduction will vary with temperature, S02 and
2 concentrations; however, virtually all SO3 will be
21 converted to SO2.
22 Excess reductant such as carbon monoxide or
23 hydrogen preC;ent in the effluent gas will reduce copper
24 oxide yresent in the effluent stream in accordance with
equation (7) below.
26 CuO + C0~ Cu + C02 (7)
27 Thus, some copper may report in the particulate materials
28 recovered from the gas particle separator 19 in the form
29 of copper metal.
Solids recovered in separator l9 are removed
::
'
~200(~
-- 6
1 via line 20 and combined, if so desired, with the calcine
2 removed from reactor 10 via line 16. Thereafter, the
3 calcine can be treated in the standard smelting operations
4 or by hydrometallurgical methods for recovery of copper
therefrom.
6 Although the present invention has been de-
7 scribed in particular detail in connection with copper
8 concentrates, other mineral concentrates may be employed
g such as those containing primarily zinc or nic~el.
Also, from the foregoing, it should be apparent
11 that certain modifications and changes can be made in
12 the present invention without departing from the spirit
13 and scope of the invention, and that such modifications
14 and variations are considered to be within the scope of
the appended claims.
,, .
