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A perspective of methods for processing of metallurgical wastes
Resources, Conservation and Recycling, 10 ( 1 9 9 4 ) 205-211
205
Elsevier Science B.V.
A perspective of methods for processing of metallurgical wastes N.A. Vatolin Institute of Metallurgy, Ural Division of Russian Academy of Science, 101 Amundsen St., Yekaterinburg 620219, Russia
ABSTRACT This report considers physico-chemical foundations and technological schemes for processing three kinds of wastes: (1) of aluminum production - red slimes; (2) processing of pyrite concentrates burnt pyrites; and (3) production of phosphorus fertilizers - phosphogypsum. The ore base of Ural's ferrous and non-ferrous metallurgy industry is represented by polymetallic raw materials resources. As a result of the non-efficient use of raw materials and imperfect technological processes, a catastrophic ecological situation has been created in the Urals: hundreds of millions of tonnes of non-ferrous metals production wastes have accumulated occupying 40000 to 45000 hectares. Each year the amount of wastes increases by 150 millions t. Similar situations take place in a number of other countries.
1. C O M P L E X P R O C E S S I N G O F R E D SLIMES
During processing of bauxites into alumina, wastes-slimes are produced. Their amount depends on output volume of alumina and makes up more than 20 million t per year. Worldwide waste production is more than 0.5 billion t. Slime storage sites are the source of alkali contamination of surface and underground reservoirs and dust. Depending on methods of processing and composition of initial bauxites, red slimes contain (mass %): 12-15 A1203; 38-51 Fe203; 10-14 CaO; 8-10 SIO2; 4-5 TiO2 and 2-7 other oxides including rare-earth metals and scandium oxide (up to 0.01 ). Cost of components of slimes is comparable with the cost of alumina extracted from bauxite. Slimes can be used in the production of construction materials, of various brands of cement, of organic-mineral fertilizers, and in ferrous metallurgy as an additive (binder) in the production of pellets or agglomerates. These are not all the ways of red slimes utilization. Moreover, in these processes many valuable components of slimes are not extracted and slimes can not be wholly used. The optimal perspective of red slimes utiliza0921-3449/94/$07.00 © 1994 Elsevier Science B.V. All fights reserved.
206
N.A. VATOLIN
tion is their complex processing with maximum possible extraction of valuable constituents. There are some interesting methods, according to which dried red slime undergoes reduction by roasting in shaft or boiling-layer furnaces. This yields products out of which after grinding it is possible to extract iron as a concentrate, and alumina and Ti; the remnant is used in cement production [ 1 ]. Other methods suggest red slime should be processed with the yield of conversion or cast pig iron and self-slaking slag with subsequent extraction of alumina. After leaching, the remnant is used for cement production [ 2 ]. The technological scheme, elaborated by the Institute of Metallurgy, Ural Division of the Russian Academy of Sciences, and tested in pilot-plant conditions (Fig. 1 ), includes several stages. In the first stage, red slime (fresh or from storage) undergoes reduction by roasting in a rotary tube furnace at 1000-1100 ° C, iron being reduced by 90-95%. The received burnt solid remnant is cooled (it is better to use remnant that has not been cooled) and put Lime
Carbonaceous
Red slime
Smelting in electric furnace
Ferrosillcium
Alumocalcium sla~
(16-20 % Si)
(50 % A1203, 25 % CaO, 5 % SiO2, 4 % TIO2, 250 g/ton Sc)
Grinding Leechilg Na2CO3+CaO'AI203
70-80°C = Na20.AI203÷CaC03
Lime slime
Aluminate solution
Acid treatment HNO3+H2S04
Alumina
production
/1\ Sc__concen_trete (up to 3 %)
G_~ ~
Calcium
Construction mater ial s
Mineral fert i I i zers
Fig. I. Technological scheme of red slimes complex processing.
PROCESSING OF METALLURGICALWASTES
207
into an electric-arc ore-thermal furnace with mixture and flux. Melting conditions (second stage) are such that Si reduces form the oxide part of the burnt remnant, dissolves in metallic iron and forms an alloy containing 1620% Si. Other oxides transit into slag containing (mass %): 46-50 A1203,2535 CaP, 5-6 SIP2, 3-4 TIP2, and 250-270 g/t Sc. According to its quality, the produced alloy can be used directly for steel production and/or instead of iron chips at ferroalloys melting. The specific feature of smelting in the electric furnace is maximum Si reduction (85-90%) and minimum transition of Ti into alloy. This is achieved by control of the electric regime of the process. At the third stage, high-alumina slag is ground, processed by soda solution at 70-80°C during 40 min, and alumina is then extracted. Soda becomes caustic: Na2 CO3 + CaP. A1203 ~ N a 2 0 . A1203 + CaCO3 with a yield of valuable caustic alkali. Lime carbonate slag that is formed is treated successively by nitric and sulphuric acids with a yield of nitric-acid Ca and gypsum. Solutions containing rare-earth metals and Sc are sent to chemical processing (fourth stage). For scheme realization, standard equipment can be used. 2. P Y R I T E C O N C E N T R A T E S , B U R N T P Y R I T E S A N D P Y R I T E TAILS
Processing of pyrite concentrates involves roasting under oxidizing conditions for S transformation into gases in order to produce sulphuric acid. All other valuable elements (Fe, non-ferrous and noble metals) transit into burnt pyrites and are lost, as they are sent either to dumps or (in a better case) are used in cement production. Pyrite (sulphide) tails from beneficiation are not presently processed at plants in the Commonwealth of Independent States, though by content of noble metals (Au, 0.72 g/t; Ag, 10.8 g/t) they are similar to pyrite concentrates (Au, 1.38 g/t; Ag, 14.2 g/t) and can be considered useful as engineering raw materials. Complex processing of pyrite concentrates (burnt pyrites) was solved along two main lines: chloride and chloride-free processing. The method of high temperature ( 1250 ° C) chloride-sublimation of burnt pyrites [ 3 ] is rather difficult and requires a high quality of burnt pyrites; an arsenic content less than 0.1% and Si dioxide less than 7.0% is desirable. Domestic burnt pyrites do not meet these demands. Among chloride-free methods, recently there were suggestions in regard to oxidation smelting of pyrite concentrates in an autogenous aggregate with a yield of matte, accumulating noble metals and Cu and slag of various corn-
208
N.AV.ATOLIN
position from ferro-silicate to ferrite-calcium [ 3,4 ]. These processes can be very successful if proper and efficient ways of slags utilization are found. The Institute conducted a complex of physico-chemical and technological investigations and on the base of their results, and offered a new technology of processing of domestic pyrite concentrates (burnt pyrites, tails), the scheme of which is shown in Fig. 2. It includes the stages of: - oxidation (autogenous) smelting of pyrite concentrates with a yield of sulphur gases for production of sulphuric acid, matte (accumulating noble metals and Cu), and convener ferroaluminous ( 15-25% A1203 ) slag; - reduction finishing of ferroaluminous slag with a yield of expensive commercial product - pig-iron (ferrosilicium) and high-alumina (melted) cement. -
Pyrite-containing material (concentrate, burnt pyrite, tails)
~ 1~ ~ A i r
Al203-containing material (non-conditlonal bauzite)
oxigen
A1203-35-45 %; CAO-20-30 %; Fe203-30-40 %: SIO2~4-6 % Aut°.qen°us rme it in~ ~ S!a B ~ FeOx-45-55 %; A1203-20-25% ; CaO-4-10%; SiO25-25%, S-0.51.5%; Cu up to 0.1%
matte (Cu-2-6%, Fe-65-67%; S-20-25%, Au-lO-80g/t, Ag-80-2OOg/t) I
\
TO non-ferrous
CaO and AI2 containing \ materi.~
Purification
metallor for Au,Ag, Cu extraction
Gases
/
For H2S04 production
1
dust
~
reducer
1
Finishin~ (electric furnace, smelting in liquid bath or blast furnace)
/
high-alumina V Tofer-
Pig iron
rous metallurgy
cement
to construction industry
gases ~
Purl fication Gases
Blow warming
dust-
gxtraction of Zn, Pb, etc.
Fig. 2. Principal technological scheme of waste-free processing of pyrite-containing materials.
PROCESSINGOFMETALLURGICALWASTES
209
Slag finishing can be done by way of: - reduction of liquid slag in an electric or Vanyukov furnace (liquid-bath furnace, LBF); reduction and melting of solid slag in a blast furnace. We recommend its preliminary agglomeration together with iron-ore raw materials in order to cause the transformation: -
(Fe)2 + (stag)~Fe3 + (agglom.) The offered technology can be used for processing pyrite-containing materials of any chemical composition, including burnt pyrites and pyrite tails stored for several years. We estimated the possibility to extract from pyrite concentrates: 90-92% S into gases ( 10-45% SO2); 80-90% Cu, 85-92% Au and 85-90% Ag into matte ( 1.5-6% Cu, 10-80 g/t Au, 80-200 g/t Ag), 80-85% Fe into pig iron (95.596% Fe, 0.01-0.02% Cu, 3.5-4% C, 0.01-0.02% S), and production of highalumina slag-cement containing 40-42% CaO, 40-45% A1203, 5-10% SiO2, 3-8% FeO. 3. PHOSPHOGYPSUM
In production of concentrated phosphor fertilizers on the base of extracted phosphor acid, the waste is phosphogypsum (PG), which forms at during decomposition of phosphate raw material with sulphuric acid via the reaction: Ca5 (PO4) 3F + 5H2 SO4 + mH3 PO4 -Faq. (m + 3 ) H3 PO4 "F 5 ( C a S O 4 • nil2 + HF + aq. Depending on decomposition conditions of phosphates, it is possible to selectively produce the dihydrate of Ca sulphate (CaSO4.2H20) and the halfh y d r a t e ( C a S O 4 • 5 H 2 0 ) . The total amount of water in dihydrate PG is 4047%, in half-hydrate 24-32%. Presently, this country stores more than 120 million t of PG and dumps occupy an area more than 1000 ha. Up to now the problem of PG utilization in the country has not been wholly solved. Technical possibilities for use of PG have been proven in production of gypsum articles, in the cement industry, in agriculture, for production of sulphuric acid, of Ca sulphide, as a filler in production of plastic, paper, paint, etc., in production of ammonium sulphate and Ca carbonate, in road construction, etc. A new and efficient use of PG is creation of sulphidizer on the base for nonferrous metallurgy (Fig. 3). Presently, during blast smelting of oxidized Ni ores, pyrite-containing materials (ore, pyrite concentrate, etc.) are used as
210
N.A.VATOLIN
sulphidizers. Efficiency of PG sulphidizcr use is achieved as a result of increased S utilization, economy of pyrite-containing material and lime, and a decrease of harmful substances discharge into the atmosphere. A higher degree of S utilization is achieved due to its more complete transformation into sulphide form: t>900°C CaSO4 + C--, CaS + CO,
CO 2
And when pyrite is used: t=450-500°C FcS2 ~ FcS + ½S2 this process takes place in upper regions of the furnace and leads to 50% loss of sulphidizer S-pyrite and contamination of atmosphere environment. Thus it is possible to optimize use of pyrite materials. Besides, CaSO4 contains Ca 2+, i.e. expenditures of CaCOa decrease. A processing is illustrated in Fig. 3.
Phosphogyps~ I
Reducer coal) ~_e,
pelletizinq Pell!ts (sulphldizer) Ni-ore
]
~ ~ S h a f t u~ace for Ni-oresmelting slaff
matte
vases
processing
refining
+!
Fig. 3. Schemeof phosphogypsumprocessing.
PROCESSING OF METALLURGICAL WASTES
211
REFERENCES 1 Process of extraction of ferrum, titanium and aluminum from the red slime. Patent of France, No. 1336621, 22.10.62/22.07.63. 2 B.Z. Kudinov, A.I. Bychin and L.I. Leontiev, Non-Ferrous Metals 1 (1967) 63. 3 0 . Jasutake, J. Metals 3 (1968) 63. 4 A.V. Vanyukov, V.P. Bystrov and A.D. Voskevich, Smelting in Liquid Bath. Metallurgy, Moscow, 208 pp. 5 A.I. Okunev, E.N. Selivanov, S.N. Shin et al., Studies, elaboration of ways of depletion and application of slags of heavy non-ferrous metals. Ginzvetmet Moscow (1984) 10.
205
Elsevier Science B.V.
A perspective of methods for processing of metallurgical wastes N.A. Vatolin Institute of Metallurgy, Ural Division of Russian Academy of Science, 101 Amundsen St., Yekaterinburg 620219, Russia
ABSTRACT This report considers physico-chemical foundations and technological schemes for processing three kinds of wastes: (1) of aluminum production - red slimes; (2) processing of pyrite concentrates burnt pyrites; and (3) production of phosphorus fertilizers - phosphogypsum. The ore base of Ural's ferrous and non-ferrous metallurgy industry is represented by polymetallic raw materials resources. As a result of the non-efficient use of raw materials and imperfect technological processes, a catastrophic ecological situation has been created in the Urals: hundreds of millions of tonnes of non-ferrous metals production wastes have accumulated occupying 40000 to 45000 hectares. Each year the amount of wastes increases by 150 millions t. Similar situations take place in a number of other countries.
1. C O M P L E X P R O C E S S I N G O F R E D SLIMES
During processing of bauxites into alumina, wastes-slimes are produced. Their amount depends on output volume of alumina and makes up more than 20 million t per year. Worldwide waste production is more than 0.5 billion t. Slime storage sites are the source of alkali contamination of surface and underground reservoirs and dust. Depending on methods of processing and composition of initial bauxites, red slimes contain (mass %): 12-15 A1203; 38-51 Fe203; 10-14 CaO; 8-10 SIO2; 4-5 TiO2 and 2-7 other oxides including rare-earth metals and scandium oxide (up to 0.01 ). Cost of components of slimes is comparable with the cost of alumina extracted from bauxite. Slimes can be used in the production of construction materials, of various brands of cement, of organic-mineral fertilizers, and in ferrous metallurgy as an additive (binder) in the production of pellets or agglomerates. These are not all the ways of red slimes utilization. Moreover, in these processes many valuable components of slimes are not extracted and slimes can not be wholly used. The optimal perspective of red slimes utiliza0921-3449/94/$07.00 © 1994 Elsevier Science B.V. All fights reserved.
206
N.A. VATOLIN
tion is their complex processing with maximum possible extraction of valuable constituents. There are some interesting methods, according to which dried red slime undergoes reduction by roasting in shaft or boiling-layer furnaces. This yields products out of which after grinding it is possible to extract iron as a concentrate, and alumina and Ti; the remnant is used in cement production [ 1 ]. Other methods suggest red slime should be processed with the yield of conversion or cast pig iron and self-slaking slag with subsequent extraction of alumina. After leaching, the remnant is used for cement production [ 2 ]. The technological scheme, elaborated by the Institute of Metallurgy, Ural Division of the Russian Academy of Sciences, and tested in pilot-plant conditions (Fig. 1 ), includes several stages. In the first stage, red slime (fresh or from storage) undergoes reduction by roasting in a rotary tube furnace at 1000-1100 ° C, iron being reduced by 90-95%. The received burnt solid remnant is cooled (it is better to use remnant that has not been cooled) and put Lime
Carbonaceous
Red slime
Smelting in electric furnace
Ferrosillcium
Alumocalcium sla~
(16-20 % Si)
(50 % A1203, 25 % CaO, 5 % SiO2, 4 % TIO2, 250 g/ton Sc)
Grinding Leechilg Na2CO3+CaO'AI203
70-80°C = Na20.AI203÷CaC03
Lime slime
Aluminate solution
Acid treatment HNO3+H2S04
Alumina
production
/1\ Sc__concen_trete (up to 3 %)
G_~ ~
Calcium
Construction mater ial s
Mineral fert i I i zers
Fig. I. Technological scheme of red slimes complex processing.
PROCESSING OF METALLURGICALWASTES
207
into an electric-arc ore-thermal furnace with mixture and flux. Melting conditions (second stage) are such that Si reduces form the oxide part of the burnt remnant, dissolves in metallic iron and forms an alloy containing 1620% Si. Other oxides transit into slag containing (mass %): 46-50 A1203,2535 CaP, 5-6 SIP2, 3-4 TIP2, and 250-270 g/t Sc. According to its quality, the produced alloy can be used directly for steel production and/or instead of iron chips at ferroalloys melting. The specific feature of smelting in the electric furnace is maximum Si reduction (85-90%) and minimum transition of Ti into alloy. This is achieved by control of the electric regime of the process. At the third stage, high-alumina slag is ground, processed by soda solution at 70-80°C during 40 min, and alumina is then extracted. Soda becomes caustic: Na2 CO3 + CaP. A1203 ~ N a 2 0 . A1203 + CaCO3 with a yield of valuable caustic alkali. Lime carbonate slag that is formed is treated successively by nitric and sulphuric acids with a yield of nitric-acid Ca and gypsum. Solutions containing rare-earth metals and Sc are sent to chemical processing (fourth stage). For scheme realization, standard equipment can be used. 2. P Y R I T E C O N C E N T R A T E S , B U R N T P Y R I T E S A N D P Y R I T E TAILS
Processing of pyrite concentrates involves roasting under oxidizing conditions for S transformation into gases in order to produce sulphuric acid. All other valuable elements (Fe, non-ferrous and noble metals) transit into burnt pyrites and are lost, as they are sent either to dumps or (in a better case) are used in cement production. Pyrite (sulphide) tails from beneficiation are not presently processed at plants in the Commonwealth of Independent States, though by content of noble metals (Au, 0.72 g/t; Ag, 10.8 g/t) they are similar to pyrite concentrates (Au, 1.38 g/t; Ag, 14.2 g/t) and can be considered useful as engineering raw materials. Complex processing of pyrite concentrates (burnt pyrites) was solved along two main lines: chloride and chloride-free processing. The method of high temperature ( 1250 ° C) chloride-sublimation of burnt pyrites [ 3 ] is rather difficult and requires a high quality of burnt pyrites; an arsenic content less than 0.1% and Si dioxide less than 7.0% is desirable. Domestic burnt pyrites do not meet these demands. Among chloride-free methods, recently there were suggestions in regard to oxidation smelting of pyrite concentrates in an autogenous aggregate with a yield of matte, accumulating noble metals and Cu and slag of various corn-
208
N.AV.ATOLIN
position from ferro-silicate to ferrite-calcium [ 3,4 ]. These processes can be very successful if proper and efficient ways of slags utilization are found. The Institute conducted a complex of physico-chemical and technological investigations and on the base of their results, and offered a new technology of processing of domestic pyrite concentrates (burnt pyrites, tails), the scheme of which is shown in Fig. 2. It includes the stages of: - oxidation (autogenous) smelting of pyrite concentrates with a yield of sulphur gases for production of sulphuric acid, matte (accumulating noble metals and Cu), and convener ferroaluminous ( 15-25% A1203 ) slag; - reduction finishing of ferroaluminous slag with a yield of expensive commercial product - pig-iron (ferrosilicium) and high-alumina (melted) cement. -
Pyrite-containing material (concentrate, burnt pyrite, tails)
~ 1~ ~ A i r
Al203-containing material (non-conditlonal bauzite)
oxigen
A1203-35-45 %; CAO-20-30 %; Fe203-30-40 %: SIO2~4-6 % Aut°.qen°us rme it in~ ~ S!a B ~ FeOx-45-55 %; A1203-20-25% ; CaO-4-10%; SiO25-25%, S-0.51.5%; Cu up to 0.1%
matte (Cu-2-6%, Fe-65-67%; S-20-25%, Au-lO-80g/t, Ag-80-2OOg/t) I
\
TO non-ferrous
CaO and AI2 containing \ materi.~
Purification
metallor for Au,Ag, Cu extraction
Gases
/
For H2S04 production
1
dust
~
reducer
1
Finishin~ (electric furnace, smelting in liquid bath or blast furnace)
/
high-alumina V Tofer-
Pig iron
rous metallurgy
cement
to construction industry
gases ~
Purl fication Gases
Blow warming
dust-
gxtraction of Zn, Pb, etc.
Fig. 2. Principal technological scheme of waste-free processing of pyrite-containing materials.
PROCESSINGOFMETALLURGICALWASTES
209
Slag finishing can be done by way of: - reduction of liquid slag in an electric or Vanyukov furnace (liquid-bath furnace, LBF); reduction and melting of solid slag in a blast furnace. We recommend its preliminary agglomeration together with iron-ore raw materials in order to cause the transformation: -
(Fe)2 + (stag)~Fe3 + (agglom.) The offered technology can be used for processing pyrite-containing materials of any chemical composition, including burnt pyrites and pyrite tails stored for several years. We estimated the possibility to extract from pyrite concentrates: 90-92% S into gases ( 10-45% SO2); 80-90% Cu, 85-92% Au and 85-90% Ag into matte ( 1.5-6% Cu, 10-80 g/t Au, 80-200 g/t Ag), 80-85% Fe into pig iron (95.596% Fe, 0.01-0.02% Cu, 3.5-4% C, 0.01-0.02% S), and production of highalumina slag-cement containing 40-42% CaO, 40-45% A1203, 5-10% SiO2, 3-8% FeO. 3. PHOSPHOGYPSUM
In production of concentrated phosphor fertilizers on the base of extracted phosphor acid, the waste is phosphogypsum (PG), which forms at during decomposition of phosphate raw material with sulphuric acid via the reaction: Ca5 (PO4) 3F + 5H2 SO4 + mH3 PO4 -Faq. (m + 3 ) H3 PO4 "F 5 ( C a S O 4 • nil2 + HF + aq. Depending on decomposition conditions of phosphates, it is possible to selectively produce the dihydrate of Ca sulphate (CaSO4.2H20) and the halfh y d r a t e ( C a S O 4 • 5 H 2 0 ) . The total amount of water in dihydrate PG is 4047%, in half-hydrate 24-32%. Presently, this country stores more than 120 million t of PG and dumps occupy an area more than 1000 ha. Up to now the problem of PG utilization in the country has not been wholly solved. Technical possibilities for use of PG have been proven in production of gypsum articles, in the cement industry, in agriculture, for production of sulphuric acid, of Ca sulphide, as a filler in production of plastic, paper, paint, etc., in production of ammonium sulphate and Ca carbonate, in road construction, etc. A new and efficient use of PG is creation of sulphidizer on the base for nonferrous metallurgy (Fig. 3). Presently, during blast smelting of oxidized Ni ores, pyrite-containing materials (ore, pyrite concentrate, etc.) are used as
210
N.A.VATOLIN
sulphidizers. Efficiency of PG sulphidizcr use is achieved as a result of increased S utilization, economy of pyrite-containing material and lime, and a decrease of harmful substances discharge into the atmosphere. A higher degree of S utilization is achieved due to its more complete transformation into sulphide form: t>900°C CaSO4 + C--, CaS + CO,
CO 2
And when pyrite is used: t=450-500°C FcS2 ~ FcS + ½S2 this process takes place in upper regions of the furnace and leads to 50% loss of sulphidizer S-pyrite and contamination of atmosphere environment. Thus it is possible to optimize use of pyrite materials. Besides, CaSO4 contains Ca 2+, i.e. expenditures of CaCOa decrease. A processing is illustrated in Fig. 3.
Phosphogyps~ I
Reducer coal) ~_e,
pelletizinq Pell!ts (sulphldizer) Ni-ore
]
~ ~ S h a f t u~ace for Ni-oresmelting slaff
matte
vases
processing
refining
+!
Fig. 3. Schemeof phosphogypsumprocessing.
PROCESSING OF METALLURGICAL WASTES
211
REFERENCES 1 Process of extraction of ferrum, titanium and aluminum from the red slime. Patent of France, No. 1336621, 22.10.62/22.07.63. 2 B.Z. Kudinov, A.I. Bychin and L.I. Leontiev, Non-Ferrous Metals 1 (1967) 63. 3 0 . Jasutake, J. Metals 3 (1968) 63. 4 A.V. Vanyukov, V.P. Bystrov and A.D. Voskevich, Smelting in Liquid Bath. Metallurgy, Moscow, 208 pp. 5 A.I. Okunev, E.N. Selivanov, S.N. Shin et al., Studies, elaboration of ways of depletion and application of slags of heavy non-ferrous metals. Ginzvetmet Moscow (1984) 10.