Refractories, Vol. 34, No. 11, November, 1993
RAW MATERIALS THE MARKET FOR MAGNESIA RAW MATERIAL
UDC 666.762.3(100)(048.1)
L. B. Khoroshavin and V. A. Kononov
The world annual production of periclase is about 11.4 million tons, of which 9.0 million tons are produced from natural magnesite and 2.4 million tons from seawater and natural brine. The annual production of periclase powder in the countries of former socialist collaboration was about 6 million tons including 2.2 in Russia, 1.4 in the Korean Peoples Democratic Republic, 1.7 in China, and 0.7 in Slovakia. The annual market for periclase powder of the industrially developed countries is about 5 million tons, including 2.5 from native magnesite (Austria, Greece, Brazil, Canada, Turkey, Spain, India, and Yugoslavia) and 2.4 from seawater (USA, Japan, Great Britain, Italy, Mexico, Ireland, and Israel). In the western countries and Japan 60% of periclase powder is obtained from seawater (brine) and 40% from native magnesite while in the countries of Eastern Europe, China, and the Korean Peoples Democratic Republic about 97 % of periclase powder is produced from native magnesite, primarily of the crystalline form. Raw Magnesite. Magnesite rock consists of the crystalline mineral magnesite (MgCO3), which contains 47.6% MgO and 52.4% CO2. The color of magnesite is white with a grayish or yellowish tint and sometimes snow-white with a glassy luster. The Molls hardness is 4.5-5 and the density 2.9-3.1 g/cm3 [2, pp. 351-352]. In nature there is a continuous series of different compounds of variable composition from MgCO3 to Fe20 3. The extreme magnesia members of this isomorphic series, magnesite with up to 2.5% iron oxides impurity and brainerite with not more than 14.5% iron oxide hnpurity, have found wide use in industry [3]. They are rarely encountered ha the form of well formed crystals but more frequently form granular aggregates. Dolomite, quartz, talc, calcite, pyrite, and other minerals are present in magnesite rock as mineral impurities. As a rule pure magnesites are not replaced in nature by products of a change 9 in them. In weathering brainerite sometimes transforms to iron oxides. Native magnesites are encountered in two physical forms, crystalline (ore magnesite) and microcrystalline (amorphous magnesite). The first form is encountered together with dolomite or lime rocks. Sometimes iron oxide impurities are encountered in the form of the mineral brainerite. The most characteristic deposits are found in Austria, Slovakia, Spain, Russia, China, Brazil, the Korean Peoples Democratic Republic, and the USA. Amorphous deposits are encountered as products of decomposition of ultrabasic rocks. The main sources of such raw material are located in Greece, Turkey, Yugoslavia, and India and they also include recently discovered deposits in Saudi Arabia and Guatemala. Large deposits of magnesite are related to certain formations and may be combined in three genetic types (Table 1). Mining Of raw magnesites is comparatively similar in the world. Abandonment of mines in Austria, Greece, and Spain has been compensated by organization of mining in Turkey, China, the Korean Peoples Democratic Republic, Slovakia and other previously nonmagnesia producing countries (Table 2). Crystalline Magnesites. Crystalline magnesite is a product of the change in limestone or dolomites obtained in action on them of solutions containing magnesium bicarbonate: CaCO 3 + Mg(HCO3) 2 =
MgCO 3 + Ca(HCO3)z,
CaMg(CO3)2 + Mg(HCO3)2 = 2MgCO 3 + Ca(HCO3)2. Amorphous magnesites are products of breakdown of magnesium hydrosilicates in action on them or water and carbon dioxide: H4Mg3Si209 + H 2 0
+ 2CO 2 = 2MgCO 3 + SiO 2 + H20.
Eastern Refractory Institute. "Shiber" Corporation. Translated from Ogneupory, No. 11, pp. 18-24, November, 1993.
0034-3102/93/1112-0561512.50 9
Plenum Publishing Corporation
561
TABLE 1. Genetic Types of Magnesia Deposits Type of deposit Hydrothermal metasomatic
Sedimentary
Infiltration
Subtype Brief characteristics
Name of deposit
A
Deposits of crystalline magnesite in dolomite rocks
Satka, Kirgiteisk, Tal'sk, Verkhnyaya Tura, Savino, Onotsk, Manjursk (Chinese Republic), Veitsha (Austria)
B
Deposits of talc-magnesia rocks in hyperbazites
Shabrovsk, Sysert' (Russia)
A
Deposits of free grained magnesite in continental sulfurous deposits
Bela-Stena, Krenma, BraneshkoPole (Yugoslavia)
Veined deposits of amorphous magnesite related to the weathering crust of serpeninites
Khalilovo (Russiai, Euboea (Greece)
TABLE 2. Mining of Native Magnesitein 1988-1990 Country
Australia Austria Brazil Canada China Slovakia Greece India N. Korea Nepal Poland S. Africa Spain Turkey USA Russia Yugoslavia Zimbabe Total
Mining of native raw magnesite, thousands of tons 1988
1989
1990
63 1122 680 ZOO 3400 2500 848 508 2500 45 24 74 473 1126 10O 4980 382 30 19055
65 1199 700 200 3500 2700 850
65 110O 700 200 3500 2800 800
480
500
3000 28 24 76 470 1199 100 4920 364 33 19908
3000 25 24 114 460 1200 100 4827 370 35 19823
In Russian the primary producer of crystalline magnesites is the Magnesite Corporation working the Satka deposit. The magnesites mined are divided into four classes and the requirements for them according to TU 14-8-64-73 are shown in Table 3. The primary impurities in crystalline magnesite are dolomite, calcite, diabase, and quartz and in amorphous serpentine and quartz. Especially harmful at present are mineral impurities containing calcium and silicon oxides. The free calcium oxide promotes hydration of the fired powders while with a low silica content (CaO/SiO2 < 2) the combined calcium oxide forms low-melting minerals (monticellite and merwinite but with a CaO/SiO2 > 2 ratio a refractory binder forsterite, is obtained. Diabase reduces the refractoriness of the material. Iron oxide impurities form magnesioferrite, which in small quantities improves sintering of the material. Native magnesites are mined by underground or open methods. The open-pit method used for mining of material from a depth of up to 60 m and therefore powerful power shovels are required. In the mines of Faicher Magnezit Werke raw magnesite is mined by the underground method. The deposit consists of individual magnesite bodies separated by layers of clay and lime shale, which requires selective working of the raw magnesite of individual quality classes. The deposits are uncovered through a staple mine shaft with galleries and through a spiral downgrade. The method of mining is extraction as a chamber with subsequent backfilling by the main ore. To maintain the worked-out space pillars remain. Working is done from top to bottom and the height of the layer removed is 3 m. The raw magnesite is removed by drilling and explosive work with use of mobile drilling trucks with a pneumatic drive. The rock is removed by diesel loaders and the large lumps are broken up in place by a mobile pneumatic chisel.
562
TABLE 3. Chemical Composition of Russian Magnesite Deposits, % Component
MgO SiO 2 CaO R203 Am calc
, Satka, magnesite of class 9
Khalilova
1
2
3
4
46,0 1,2 0,8 1,0 51,0
45,0 1,5 1,2 2,1 51,2
43,0 2,4 2,8 2,5 49,3
39,0 2,5 7,0 3,0 49,0
46,4 0,9 0,4 0,7 51,6
Tal'skoe
Savino
46,2 0,6 1,2 1,5 50,5
45,9 2,4 0,7 1,7 49,2
TABLE 4. Properties of Sintered Periclase Powders from Crystalline Magnesites and Kul'dur Brucite Country
Russia
Greece Brazil China Turkey
Form (deposit)
Satka Kaktolginsk Larginsk Tal'sk ~ Kul'dur Femicko Magflot Magnezita M20 Future Cutosan Kuvas
Content, %
CaO/SiO 2 Density, glcm 3
MgO
CaO
SiO 2
95,5 95,0 95,0 95,0 96,0 95,5 95,7 94,5 98,0 96,6
1,65 2,2 2,3 2,5 2,0 1,6 2,3 0,8 0,8 1,5
0,8 0,7 0,7 1,3 1,0 2,6 0,55 1,3 0,6 1,3
2,1 3,0 3,3 1,9 2,0 0,6 4,1 0,6 1,3 1,1
3,38 3,35 3,35 3,35 3,40 3,35 3,46 3,35 3,40 3,40
The magnesite is delivered by rail to the staple shaft. After raising in the shaft to the ground level the magnesite is delivered by rail to the crusher. First the material is crushed by a jaw crusher with complex oscillation of the moveable jaw to a size of 0-300 mm and then in an impact reflective mill to a size of 0-80 mm. After grinding the raw magnesite processed by individual quality classes is delivered to a bunker for storage and from there by an aerial ropeway to the concentration plant. It is economically most desirable to work deposits of coarse crystalline magnesite. The deposits extend to a great depth and open pit or underground mining may be used. The disadvantages of the deposits are related to the size of the crystals, the presence of impurities (dolomite, lime, iron, etc.) which are difficult to remove, and the presence of pores in the sintered periclase. The chemical composition is not stable and various methods of concentration are required. Upon reaching a sufficiently high volumetric density of the periclase growth of the crystals of it or an increase in average diameter is directly proportional to the rate of grain boundary migration while the rate of grain boundary migration is inversely proportional to the radius of curvature of the grain boundaries. The distribution of impurities along the boundaries has a complex influence of grain boundary migration. Certain impurities, particularly additions of zirconium oxide, may significantly increase the diameter of periclase crystals. Many magnesites must be cleansed of impurities and of the compounds dolomoite, quartz, chlorites, serpentine, phlogopite mica, magnesite, pyrite, etc. Depending upon the conditions of use different magnesite fractions are concentrated by different methods. Magnesite is blended, magnetically separated, concentrated in heavy suspensions, and treated by flotation. Concentration in heavy suspensions makes it possible to remove dolomite impurity, which is less dense than magnesite, from the rock (mixture of magnesite and dolomite) in an aqueous suspension ferrosilicon. A high-quality concentrate containing 4546% MgO, 0.5-0.8% SiO2, and 0.8-1.2% CaO is obtained from raw material with a dolomite impurity content of up to 15% with a degree of removal of 90%. To obtain high quality products flotation is necessary. The essence of the method is the different wettability and adherence of magnesite and the impurities toward the flotation reagents (a mixture of commercial fatty acids). In use of this method preliminary grinding of the magnesite to 0.1-0.2 mm is necessary. Depending upon the original material in flotation the MgO content in the final product increases to 96.5% and the SiO 2 content may not exceed 0.1-0.3%. The CaO content drops by three to six times. In the Faicher Magnezit Werke plant raw magnesite is contaminated with dolomite, slate, and quartz while the carriers of lime and silicic acid are partially finely combined, which requires fine breaking up. Only flotation is used for concentration. The mixture of magnesite from different bunkers is first ground in a Simon-type granulator to a lump size of not less than 10 563
TABLE 5. Properties of Sintered Periclase Powders from Amorphous Magnesites Country
Greece Greece Oreece Turkey
Company
Composition, *1%
Density, g/cm3
Firing _ furnace .2
MgO
CaO
SiO2
FeaO3
AI203
95,7
2,2
1,30
0,84
0,06
3,45
Rot
96,0
2,4
0,60
0,65
0,05
3,40
Sh
95,5
1,6
2,60
0,08
0,12
3,46
Rot
96,6
1,5
1,25
0,35
0,04
3,40
Rot
Magnochrom 95,5 MK 1 HC1 98,0 Salem 92,0
2,0
1,70
0,60
0,20
3,35
Rot
2,0 2,0
0,50 5,50
0,20 0,20
0,20 0,20
3,43 3,30
Sh Rot
Fimisco E21A Fimisco Magflot Yerakini Per A Citosan Kuvas
Yugoslavia Australia India
*lln all of the compositions the B203 content is 0.01%. *2Rot - rotary; Sh - shaft. TABLE 6. Chemical Compositions of Chinese Magnesites Province
Liaoning
Shandong Sichuan Hubei Nei Monggol
Company
Haicheng Dashiqiao Xiuyan Fengcheeng Kuangdian Zhuanhe Fushun Yexian Guixian Xintai
Content, % MgO*
CaO
SiO2
Fe20 s
47,35/97,15 46,19/Not deter. 46,75/Not deter. 46,89/95,75 47,03/96,37 47,53/97,51 44,95/96,37 46,55/92,67 46,63/93,24 44,19/89,94 42,48/88,48
0,54 0,73 0,84 1,17 1,31 0,63 1,46 0,56 1,89 2,26 3,96
0,40 0,66 0,72 0,63 0,22 0,30 1,74 1,88 0,80 0,38 4,15
0,34 0,17 No information 0,25 0,20 0,26 0,73 0,70 0,50 2,17 0,85
AI20 a
0,03 0,04 0,02 0,53 0,54 0,19 0,13 0,13
*The first figure is for raw magnesite and the second for fired. mm and then wet ground in rod and ball mills with a rake classifier between them. The discharge of the classifier for removal of the sludge is supplied to a cyclone. The upper product of the cyclone is delivered to the railings and the lower is returned to the production flow. Removal of the sludge is important for successful separation in the subsequent flotation process since otherwise the selectivity of the process would be lower. In addition SiO 2 is concentrated in the sludge removed and a portion of it has already been removed before the start of the flotation process. The flotation process of separation occurs in two stages. In the first stage silicates with a stratified radical float off and in the second stage in a two-step flotation process the magnesite is retained in the form flotation concentrate while the dololIiite remains in the tailings. Fatty acids and tall oils are used as the reagents. The flotation concentrate contains about 0.35 % SiO2 and 1.5% CaO. The yield of the concentrate is 70% and the capacity of the flotation unit 500 tons per shift. Centrifuges with a solid rotor and periodic unloading of the separated material with use of a scraper are used for separation of the concentrate. This provides a reduction in moisture to 7%. The filtered water from the centrifuges is delivered to a clarifier and the lower product is returned to the centrifuges. Abroad and in Russian deposits of crystalline magnesite with a high magnesium oxide content of great promise are known. However, in our country the level of technology and insufficient f'mancial resources do not make it possible to actively develop them at present although abroad similar deposits are being successfully worked (Table 4). From Table 4 it may be seen that Satka magnesites concentrated by the flotation method, native magnesites of the Larginsk, Koktolginsk, and Tal'sk deposits, and also thermally concentrated Kul'dur brucite are competitive with foreign concentrated magnesites. Amorphous (Microerystalline) Magnesites. Amorphous magnesites of the Khalilovo deposit are widely distributed in the Southern Urals and in Kazakhstan (Donskoi Mining and Beneficiation Combine) but they have not been developed
564
TABLE 7. Properties of Chinese Flotation Magnesites Province
Haicheng
Exian
Type
Content, %
Unconcentrated Concentrate 1 Concentrate 2 Concentrate 3 Tailings Grain I Concentrate
MgO*
CaO
SiO2
Fe203
AlzO3
46,91/96,94 47,25/98,40 47,10/97,68 46,40/95,33
0,51 0,39 0,62 0,84 0,69 0,42 0,34
0,44 0,05 0,08 0.52 2,25 0,88 0,06
0,43 0,30 0,39 0,84 0,19 0,55 0,43
0,10 0,03 0,03 0,07 0,44 0,18 0,02
45,64/91,63 46,43/95,22 47,28/98,23
*First figure is for raw magnesite and the second for ftred.
TABLE 8. Characteristics of Periclase Powders Class
Wt. % CaO:SiO 2 MgO, rain
Density, g/cm3, rain
LCA1 A1 B1 B2 C1. FE
97 97 96 95 90 85
3,43** 3,40 3,33 3,25 3,10 3,20
>4:1 >3:1 >2.:1 <2:1 <2:1 >2:I
*Wt. % Fe203 is 4% maximum. **Crystal size is 110/zm minimum.
TABLE 9. Production of Different Forms of Periclase Powders in 1991, Thousands of Tons Continent
From native magnesite
From seawater (clinker)
fused
sintered
caustic
fused
sintered
caustic
Europe America Asia, Australia
12 14 21
4404 360 3323
411 151 288
13 30 -
585 810 620
207 45 60
Total 9
47
8087
850
43
2015
312
commercially since they contain 20-25 % serpentinite ores. Despite the occurrence of magnesite close to the surface and the possibility of open pit mining large expenditures for concentration of the ore are necessary. In addition the size of the crystals is 5-7/zm, which reduces the refractory properties. Native amorphous magnesites must be effectively concentrated. Normally they have a low iron oxide content and do not contain boron. In sintering the impurities form individual inclusions and are not distributed over the whole volume of the material, In sintering of the powders high-density parts with a small volume of pores are obtained. The average crystal size of the periclase is 100-200 izm, Despite the satisfactory service properties (high MgO content, low B203 and Fe203 content, high density, large average crystal size, etc.) mining of such magnesites is difficult as the result of the low yield of the ore with respect to gangue. Despite their wide distribution in the world, such types of deposits are basically ineffective as the result of the high costs in development (Table 5). 565
TABLE 10. World Production of Periclase Powders with Capacities in 1991 Country
Company
Capacity
. Powder from brine
native Europe and the Mediterranean Austria
275,0 45,0 80,0 45,0 12,0 110,0 17,0 45,0 700,0 26,0 30,0 30,0
Sintered Caustic Sintered Caustic Fused Sintered -Caustic Sintered Caustic --
Famisco-Financial Mining Grecian Magnezit Co.
300,0
Sintered
180,0 30,0 30,0
Ireland
Magnomin General Mining Mining Trading Manufacturing Premier Periclase
Sintered + caustic Sintered Caustic
100,0
-
Israel
Dead Sea Perielase
60,0
--
Slovakia France Germany Greece
Veitscher Magnezitwerke Magindag (Steirische rag) Radex Tiroler Magnezit Magnifin Magnesia Magindag Steirische Slovenska Magnezitove Zavody Cie des Salins du Midi VEB Kombinat Kali
I0,0 13,0
Italy
Sardamag Nuova Sardamag Eraclit Venier Billiton
60,0 5,0 65,0 25,0 100,0
Netherlands
-Caustic -
Norway Spain
Norsk Hydro Magnezitas Navarras SA Magnezitas de Rubian
105,0 70,0 60,0 70,0
Sintered Caustic "
Turkey
Kumas-Kutahya Manyezit Manyezit AS Comag-Continental
144,0 80,0 30,0
Sintered
20,0 35,0
Sintered
Great Britain
Madencilik Minero Mining Trade Co. Inc. Konya Krom Magnezit Steetley
Caustic + raw Caustic
200,0
-
Russia
Magnesite
2160,0
Sintered + Caustic Fused
Yugoslavia
Bogdanovich Refractory Corporation SAR Magnochrom
15,0 8,0 7,0 200,0 40,0
--
m
Caustic
Caustic Caustic from potash:
Sintered + Caustic Sintered Caustic Fused (from brine) Sintered Caustic Sintered Sintered (from brine) Caustic
Sintered + Caustic
Sintered Caustic
9 America USA
Martin Marietta Chemicals
275,0
Harbison" Walker Refractories National Refractories American Premier
200,0
--
135,0
--
100,0
Sintered + Caustic
50,0
566
Sintered + Caustic
m
Sintered + Caustic
T A B L E 10 ( c o n t i n u e d ) Country
Capacity
Company
Powder native
Brazil
Marine Magnesium Mineral Corp.
15,0 30,0
Caustic Caustic + . fused
Morton Chemical Co. Woodville Lime
10,0 5,0
Caustic Caustic (dolomite)
Baroroft Magnezita SA
5~0
IBAR Canada
Dresser Industrias Canada Baymag Mines
Magnaq Mexico
from brine
Quimica del Mar SA de CV Quimica del Rey SA de CV
140,0 32,0 60,0 13,0 60,0
Sintered Caustic Sintered Caustic Sintered '
100,0 14,0 6,0 55,0
Caustic Fused Caustic Sintered
5,0 95,0
Caustic Sintered
5,0
Caustic
Far East Australia, Africa Japan
Ube Chemical Industries Shin-Nihon Chemical Ind. Asahi Glass
450,0
Sintered
50,0 100,0
Caustic Sintered + Caustic
20,0
Sintered Caustic Sintered + Caustic
10,0 Republicof Ko~a
Sam Hwa Chemical
50,0
India
Dalmia Magnesite Corp. Tamil Nadu Magnesite
42,0
Buxna Standart
China
Almora Magnesite Himalayan Magnesite Mineral Pon Kumar Magnesite Salem Refractories Lioning Magnesite Works
Korean Peoples Korean Magnesite Democratic Republic Works The Causmag Ore Co. Australia Queensland Magnesia Pty Zimbabwe Nepal South Africa
Gatooma Magnesite Nepal Orind Magnesite Veref Mining
30,2 19,5 42,0 9,0 24,0 10,5 45,0 7,5 27,0 1450,0
Sintered Caustic Sintered Caustic Sintered
200,0 1400,0
Caustic Sintered + Caustic 10,0 Sintered 20,0 Caustic 150,0 Sintered 30,0 Caustic 21,0 Fused No. info. Raw 50,0 Sintered 35,0
567
China mined 3.4 million torts of the 19.6 million tons of magnesite mined in the world in 1987. China has many magnesite deposits, the largest of which are located in Shandong Province and are worked by the open pit method [4]. Other sources of magnesia raw material are deposits in Sichuan, Hubei, Gansu, and Nei Monggol Provinces. The Chinese magnesites from Sichuan and Shanxi have a microcrystalline structure and from the southern portion of Shandong a crystalline. They contain silicon, calcium, and iron oxide impurities. The chemical compositions of Chinese magnesites of different deposits are shown in Table 6. For the purpose of increasing magnesite quality recently wide use has been made of a two-stage flotation process making it possible to remove the hydrophobic impurities talc and other silicate minerals. The flotation process is less effective with a high calcium oxide impurity content. Flotation plants have been built in Haicheng and Exian in Liaoning province. The properties of the flotation concentrates are given in Table 7. Use of Raw Magnesite. The main areas of use of raw magnesite are the refractory and steel industries. In the refractory industry it is ftred for further use as ftred powder in production of parts and compounds. In the steel industry raw magnesite may be added in small quantities to fired powders for patching of the hearths of steel melting furnaces and may be used in guniting of steel producing equipment and also in the production of magnesia refractory materials. Raw magnesite has few areas of commercial use, one of which is production of metallic magnesium. In Becancour, Quebec, Canada Norsk Hydro Company has constructed a plant for an annual production of 60,000 tons of metallic magnesium from Chinese magnesite and Alberta Natural Gas Company and Magnesium International Corporation have jointly constructed a plant in Alberta, Canada for the annual production of 12,500 tons of metallic magnesium. In 1990 the production of metallic magnesium reached 261,000 tons with Canada and the USA producing 63%. In 1990 in Canada the cost of 1 kg of metallic magnesium was $4.40 and in the USA $3.00-3.66. In the foreign market high-quality periclase powders are divided into six groups (Table 8). In relation to heat treat temperature of the raw materials, raw magnesite and marine brine (water and brines) are subdivided into the following forms: fused - above 2825~ s i n t e r e d - 1600-2000~ caustic - average temperature 900~ In addition periclase clinker and chemically pure magnesia are produced from seawater and brine (Tables 9 and 10). As of January 1, 1992 8,984,000 tons of sintered periclase powders were produced from native raw material and 2,370,000 tons of powders from seawater and brine (Table 10). Fused periclase powders have found wide use in the refractory industry. They are primarily used in parts which must have high slag resistance, capacity for heat transfer, and specific electrical resistance. However, the high cost as the result of large electrical consumption limits their use and they are used in cases in which improved operating characteristics of the process are created. Fused and sintered periclase are used in production of periclase-carbon parts for critical areas of linings. Fused periclase is the main element of domestic heating appliances (kettles, irons, stoves, electrical samovars, etc.). Periclase in combination with other refractory oxides forms a number of refractory compounds which have found use in refractory production. Such compounds include fused noble and chrome spinels. In the steel melting industry parts, compounds, and powders of sintered periclase powders satisfying existing requirements of the industry are used for furnace linings. Periclase may be sintered to a density of 3.2-3.3 g/cm 3 with electrical consumptions of 9.2-10.5 kJ/t0n. With the introduction of oxygen converters in Japan, the USA, and Western Europe only a small portion of crystalline magnesites satisfy the requirements of the quality standard. Sintered periclase powder is used for patching the hearths of steel furnaces. In the last decade the main area of its use has become the production of periclase-carbon refractories, which as the result of the direct bonds between magnesium oxide and graphite possess high resistance to slags and metals and improved thermomechanical properties. The life of periclase-carbon refractories under high temperature conditions is several times greater than that of traditionally used parts. Caustic periclase powder produced both from native and from synthetic raw material has a large demand in the market. It is used as additions in electric melting of steel and in water treatment, in plant produced construction slabs, for the production of fertilizers and animal feed, in the pharmaceutical industry and fireproof coatings, and in various chemical industry operations. The market for periclase clinker from seawater satisfying 85 % of the requirements of users has increased. With low fuel costs and low costs for transportation of seawater or brine until 1980 the production of periclase clinker was economically 568
desirable. However, the increase in costs for energy in the 80's required improvemems in the method of production of periclase clinker with use of filters under pressure (dehydration) and high-temperature shaft kilns under pressure, with use of which the energy costs are 40-50 % of those necessary with use of rotary kilns, etc. Chemically pure magnesite is used in especially critical applications such as for coating of tra~former steel, the production of special types of rubber, perfumery and cosmetics, chemical reagents, crucibles for melting of rare-earth and precious metals, and other purposes.
REFERENCES
.
2. 3. 4.
B. Coope, "Magnesite and magnesia, industrial minerals, minerals," in: Metals and Minerals Annual Review (1991), pp. 115-116. K. K. Strelov, I. D. Kashcheev, and P. S. Mamykin, The Technology of Refractories [in Russian], Metallurgiya, Moscow (t988). V. P. Petrov, Nonmetallic Mineral Resources of the USSR (Handbook) [in Russian], Nedra, Moscow (t984). Xun Yu Liang, Zi Shan Rong, and Ski Chang Feng, Magnesite Refractory in China - General Survey and Outlook, Unitecr. (1989), pp. 486-495.
569
