The crude renewable raw materials into metallurgical lead is substantially Fire blast furnace and smelting furnace. Reverberatory furnaces and rotary kiln smelting are rarely used. The necessary condition for the smooth operation of the blast furnace smelting is to preliminarily granulate (-20) millimeters. In the metallurgy of lead, a sintering method at a high temperature is usually employed for this purpose. This process is done on a linear sintering machine. The sintered material may consist of a raw material and a recycled material or a recycled material with a returning additive.
The main components of the fine-grained materials are the powders dismantled from the waste lead storage batteries, the lead oxide skin, the residue of the dust removal equipment , the lead paste, the oil and soil, and the lead-containing filter residue for producing zinc .
A sintering charge is provided in accordance with the conditions for producing a self-welding agglomerate. The co-sintering of the recycled material and the sulfide component is completed according to the process flow shown in FIG.
The production of self-fusing agglomerates must be guaranteed. The composition of the charge usually consists of sulfides and oxides of primary and recycled raw materials, iron flux and limestone .
The high return rate is a prominent feature of the self-melting agglomerate. In fact, the return rate accounts for 65 to 70% of the total charge. The sulfur content in the sulfide in the charge should not exceed 6.5 to 8.0%. Higher sulphur content leads to increased exotherm and pre-burning of the charge components, which makes the next metal sulfide chlorination difficult. Sulfur in the smelting charge cannot be completely removed, resulting in loss of lead in the sulfide phase and a reduction in the recovery of lead into crude lead.
Desulfurization is accomplished by a method of heating the charge in an oxidizing atmosphere at a temperature of 1000 to 1100 ° C during the sintering process.
The oxidation of sulfides is carried out as follows:
MeS+2O 2 â†â†’MeSO 4 (1)
MeS+1.5O 2 â†â†’MeO+SO 2 (2)
Dissociation of high-priced sulfides is possible, and the dissociated product is gaseous sulfur. The sulfur vapor oxidizes in the presence of oxygen to form SO 2 . Metal sulfate dissociation is accompanied by the precipitation of sulfur trioxide (sulfuric anhydride SO 3 ):
MeSO 4 â†â†’MeO+SO 3 (3)
Figure 1 Flow chart of sintering equipment for lead materials
1-feed yard of lead-containing material; 2-flux material yard; 3-hopper type batching field; 4 -crush crusher ;
5-conical crusher ; 6-vibrating screen; 7-disc granulator; 8-sintering machine;
9-single-roller pulverizer; 10-lifting machine; 11-cyclone dust collector; 12-four-roller pulverizer.
According to the reaction formulas 171 to 173, the gas phase contains O 2 , SO 2 , and SO 3 , and the relationship between them is determined by a reversible reaction:
2SO 2 +O 2 â†â†’2SO 3 (4)
The equilibrium constant of this reaction is:
K flat = P 2 SO3 / (P 2 SO 3 · PO 2 ) (5)
The partial pressure of oxygen in the gas phase can be determined by the following formula:
PO 2 = | ( | PSO 3 | ) 2 | 1 | (6) |
PSO 2 | K flat |
Figure 2 Pb-SO system thermodynamic state diagram [next]
The thermodynamically stable state of the two solid phases of PbS and PbSO 4 is characterized by a temperature below 700 °C. Reflected by line 1 under equilibrium conditions. As the temperature increases, above 700 ° C, lead sulfate dissociation:
PbSO 4 â†â†’PbO+SO 3 (7)
The equilibrium condition of this reaction is indicated by line 2. At temperatures above 700 ° C, the reaction develops as:
PbS+1.5O 2 â†â†’PbO+SO 2 (8)
The sulfide stability of lead is lower than line 3; the lead oxide produced is higher than line 3 but lower than line 2.
Solid phase interaction of lead sulfate and lead sulfide may occur near point A (700 ° C):
PbS+3PbSO 4 â†â†’4PbO+4SO 2 (9)
The lead oxide melts above 886 ° C and undergoes thermal dissociation (line 4). According to line 5, to maintain the equilibrium condition of lead sulfide to continue oxidation reaction, metal lead is formed:
PbS+O 2 â†â†’Pb solution +SO 2 (10)
Solid-phase interaction of lead sulfide and lead oxide near point B (below 886 °C):
PbS solid +2PbO solid â†â†’3Pb liquid +SO 2 (11)
The enhancement of the solid phase interaction is confirmed by the high SO 2 equilibrium partial pressure value (13.3 kPa at 800 ° C and 101 kPa at 850 ° C).
It can be seen from the analysis conducted that the thermodynamically stable lead sulfide oxidation product is lead sulfate at a temperature lower than 700 ° C; the lead oxide is stable under higher temperature conditions.
The necessary condition for the formation of lead oxide is that the concentration of SO 3 in the calcined gas (PSO 3 ) gas is low, and therefore, the pressure of dissociation of the metal sulfate is expressed by an inequality:
(PSO 3 ) gas <(PSO 3 ) sulfur
Therefore, the essence of the sinter roasting of the recycled lead material (along with the sulphide material) is that the furnace material strongly absorbs air and rapidly oxidizes the sulphide. The sulfur-containing gas generated during oxidation is immediately removed, and the production of sulfate is largely excluded.
The existing practice of sintering roasting ensures that the desulfurization rate is 75-85%, and the remaining sulfur content is not higher than 1.5-2.0%. When the sulfide is oxidized, heat is released, and the heat is sufficient for the process to be natural. When the sulfide is insufficient, the coke powder should be added to the charge. Its consumption of 1 kilogram is equivalent to less than 2 kilograms of sulfur in the sulfide.
An important factor in properly organizing the sintering process of the charge is the use of flux. The flux has a particle size of no more than 8 mm and consumes 23 to 24% of flux per 1 ton of finished agglomerate.
Limestone, iron-containing and quartz -containing materials are used as temperature-regulating fluxes. The flux promotes separation of the charge and absorbs excess heat to ensure good gas permeability.
Limestone dissociates with heat absorption at 910 °C. The iron ore, together with the flux containing quartz in the sintering charge, has a temperature-regulating property, so that the slag of the specified composition can be obtained in the subsequent blasting flux. [next]
The main liquid phase formed during sintering is lead silicate. It begins to melt at 750 ° C:
2PbO+SiO 2 =2PbO·SiO 2 (12)
PbSO 4 + SiO 2 = PbO · SiO 2 + SO 2 + 0.5O 2 (13)
Similarly, lead ferrite is formed at this temperature:
PbSO 4 +Fe 2 O 3 =PbO·Fe 2 O 3 +SO 2 +0.5O 2 (14)
PbO+Fe 2 O 3 =PbO·Fe 2 O 3 (15)
At higher temperatures, the lead silicate-silicate solution dissolves free lead and iron oxides. When cooled, lead silicate and lead ferrite are crystallized from the melt, and most of the melt condenses into a glass body.
The optimum content of lead in the calcining furnace charge should be maintained at a level of 35 to 40%. The high lead content causes many lead to appear in the metal and oxide state during sintering. At this time, lead increases with gas loss. In addition, the metal lead may melt, and the molten lead penetrates into the pumping chamber through the sintering, which reduces the strength of the sintered block and increases the loss of lead. The method of adding 200-250% of the returning sinter of the coarse charge is used to ensure the specified content of lead in the frying. At this time, the gas permeability of the charge is increased.
In order to achieve the best sintering technology and economic indicators, it is necessary to make the charge water 6 to 8%. After the water evaporates, the porosity of the charge is increased and the temperature is adjusted.
The granules of the recycled material without the raw material are characterized by a slightly different chemical composition and phase composition from the lead sulphide concentrate. In battery fragments and recycled lead materials, lead is present in the form of oxides and sulfate compounds. X-ray and chemical analysis were used to determine more than 20 compounds in the regenerated feed. In addition to lead, there are also ZnO, Sb2O5, Al2O3, SnO2, CaO, FeO, organics and other compounds.
Table 1 lists the chemical composition of the recycled lead material sent to the “Ukrainian Iron and Zinc Plant†for sintering.
Table 1 Chemical composition of recycled lead materials (%)
Recycled material | Pb | Sb | Sn | FeO | CaO | SiO 2 | Al 2 O 3 | Cl | other |
Lead slag | 65～92 | 0.5 to 10 | 0.1~1.0 | 2 to 4 | 2 to 10 | 5~16 | 2 to 6 | 0.5 to 1.0 | 0.25 |
Dust collecting mud | 50-600 | 0.5 to 1.2 | 0.5 to 2.5 | 2 to 4 | 1 to 2 | 3 to 6 | 2 to 4 | 12 to 16 | 5~12 |
Slag and sulfur | 13~35 | 0.5 to 2.5 | 0.2 to 0.6 | 4~12 | 3 to 6 | 10~16 | 3 to 5 | 1.0 to 2.0 | 1 to 6 |
Lead paste | 30～75 | 0.1 to 0.5 | 0.1 to 0.8 | 3 to 4 | 4~6 | 6~12 | 2 to 4 | 0.5～2.0 | 2 to 6 |
Moisture-proof soil | 1 to 10 | 0.1 to 0.5 | - | 1 to 3 | 1 to 3 | 14～18 | 6-8 | - | - |
Only the recycled materials in the sintering charge are: 30 to 35% of the lead-containing raw material fine particles; 7 to 12% of the pyrite slag; 5 to 8% of the calcium hydroxide; 30 to 40% of the returned sintering block; and 10 to 15 of the water-crushing residue %; 2 to 2.5% of the end of the coke. The charge of the charge increases the gas permeability and reduces the formation of the liquid phase. In order to avoid lead melting, the lead content in the charge is kept at 25 to 35%.
When the recycled material is sintered, the sintering of the charge is basically carried out by the heat generated when the fuel is burned. Studies conducted by AE Tularchenko's AE Guriev showed that the heat required for the sintering process of the recycled lead material is 50% higher than the raw material, considering the high water content of the charge and the presence of chlorides and organic impurities. During sintering, the chloride is transferred to the gas phase for 20 to 50%, and the impurities are transferred to the gas phase for 35%. These two substances then condense in the flue. The content of chlorine in the sintering flue gas is 25%, and the content of organic impurities is 20%.
The particle size and consumption of the coke powder have an effect on the sintering results. As the coke powder is ground, its consumption is reduced and the temperature of the sinter layer is increased. At this time, the strength of the agglomerate is proportional to the temperature of the layer. The relationship between the yield of qualified sintered blocks and temperature is as follows:
q=0.634t (16)
Where q----the yield of qualified agglomerates (%); t---the temperature in the sinter layer.
When the particle size of the coke powder is 2.5 to 0 mm, a better sintering index can be obtained.
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