EVALUATION OF INDIAN IRON ORE FOR DIRECT-REDUCTION PELLETS

Transcription

1 NRRI/TR-91/26 June 1991 Technical Report NRRI/TR-91/26 CMRL/TR EVALUATION OF INDIAN IRON ORE FOR DIRECT-REDUCTION PELLETS By Harold E. Goetzman Natural Resources Research Institute University of Minnesota Duluth 5013 Miller Trunk Highway Duluth, MN Coleraine Minerals Research Laboratory One Gayley Avenue PO Box 188 Coleraine, MN 55722

2 This publication is accessible from the home page of the Coleraine Minerals Research Laboratory or Economic Geology Group of the Center for Applied Research and Technology Development at the Natural Resources Research Institute, University of Minnesota, Duluth ( or as a PDF file readable with Adobe Acrobat 6.0. Date of release: March 2012 Recommended Citation Goetzman, H.E., 1991, Evaluation of Indian iron ore for direct-reduction pellets: University of Minnesota Duluth, Natural Resources Research Institute, Coleraine Minerals Research Laboratory, Technical Report NRRI/TR-91/26, 24 p. Natural Resources Research Institute University of Minnesota, Duluth 5013 Miller Trunk Highway Duluth, MN Telephone: Fax: shauck@nrri.umn.edu Web site: by the Regents of the University of Minnesota All rights reserved. The University of Minnesota is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.

3 EVALUATION OF INDIAN IRON ORE FOR DIRECT-REDUCTION PELLETS By Harold E. Goetzman June 18, 1991 Prepared for: Davy Dravo Contract Grasim Project CMRL!TR Natural Resources Research Institute University of Minnesota, Duluth 5013 Miller Trunk Highway Duluth, Minnesota 55811

4 INTRODUCTION Davy Dravo has a contract with Grasim Industries, Ltd. of Bombay, India to conduct a feasibility study for a proposed iron ore palletizing plant. This plant will utilize Indian iron ores as feed material and will produce iron-oxide pellets suitable for feeding an HYL Ill direct reduction plant. As part of this feasibility study, a contract was given to the Coleraine Minerals Research Laboratory (CMRL) to perform the required laboratory test work that would provide design information for a possible beneficiation plant, grinding circuit, and palletizing plant. RAW MATERIALS The iron ore samples tested in this program were shipped from India via airfreight. Procurement of the samples was handled by Davy Dravo. The three 50 kg samples were designated as Mineral Sales Private, LTD - ROM fines, NMDC Donimalai - iron ore fines, and Bellary Hospet Pvt - Ramandburg fines while the bulk 2-ton sample was designated as NMDC Donimalai - fines. Additives used in the palletizing tests were obtained locally from supplies available at CMRL. These included clay, bentonite, limestone, dolomite and coke breeze. TEST PROGRAM AND PROCEDURES The primary objective of the test program was to determine the conditions required to produce a high-quality iron ore pellet from the Indian iron ores available to Grasim. These pellets were to specifically be suitable for use in a direct-reduction plant. In addition, the program included a physical, chemical and grindability evaluation of the potential ores that could be purchased by Grasim. Beneficiation tests were conducted when necessary to provide information on the feasibility of upgrading the pellet feed to direct-reduction quality. Bench-Scale Tests The bench-scale test program used standard laboratory techniques for performing size analyses with chemical analyses for Fe, Si0 2, and Al on each fraction. Analyses for Cao, MgO, N~O. K 2 0, and P were also carried out on the head samples. For each sample a 200-mesh grindability work index was determined using the Bond mill. Beneficiation tests were conducted with the Wilfrey 3-ft table and the Jones wet highintensity magnetic separator (WHIMS). WHIMS tests were run at three different settings of 1 O, 15, and 20 amps which corresponds to 9000, 10,000 and 11,000 gauss. A plate gap of 2.5 mm and a feed density of 20 percent solids were used in all of the tests. The 1

5 feed was prepared to minus 20 mesh, minus 48 mesh, minus 65 mesh, and minus 100 mesh to investigate the liberation characteristics. Pot-Grate Tests The palletizing feed was prepared by open-circuit dry grinding in an Allis-Chalmers vibrating ball mill after crushing the iron ore fines to minus 10 mesh in a rolls crusher. This mill was also used to grind the limestone and dolomite for addition to the pellet feed. The coke breeze was batch ground to minus 100 mesh in a laboratory mill. Production of green balls for the pot-grate.tests was carried out by a standard procedure. Binder and flux additions were calculated on a dry basis as a percentage of the concentrate weight. Approximately 300 pounds of concentrate and the appropriate amount of additives were added to a Simpson mixer-muller and mixed for several minutes. Water was added to bring the dry mix to 8 percent moisture and then the wet mix was balled in a laboratory 36-inch-diameter disc with alternating additions of spray water and feed. After a sufficient number of pellets had formed, the load was removed from the disc and screened. The minus 1/2-inch plus 7/16-inch balls were stored in a closed container until the necessary 140 pounds for a pot-grate test was produced. A sample of the green balls from each test was reserved for moisture analysis, compression, and drop tests. Twenty balls were used for each of these quality tests. The green balls were transferred to a McKee-type pot-grate apparatus for induration. This apparatus consists of a 1-sq-ft cross sectional area, 16-inch deep, refractory-lined pot with grate bars to support the charge. The pot has a windbox and hood with attendant fan and combustion chamber to supply the processing gases. Oxygen is added to the combustion gases to give an oxidizing atmosphere during preheating and firing (about 15% 0 2 ). The apparatus has thermocouples for controlling the temperature and to indicate the bed-temperature profile. Pressure taps are provided to maintain the desired constant pressure drop during processing. A 12-inch bed of green balls was charged to the pot atop a 4-inch hearth layer of fired pellets. The sequence of firing was updraft drying, downdraft drying, downdraft preheating, firing, and recuperation at the desired temperatures. After updraft cooling, the pellets were removed from the core of the bed to avoid wall effect and samples were split out for product-quality tests, such as compression, tumble, reducibility, low-temperature breakdown, and chemical analyses. The tumble tests were by the standard ASTM procedure on a 25-pound sample. The sample is charged to a 3-ft-diameter drum (2 lifters) and rotated for 200 revolutions at 24 rpm. After tumbling the material was screened and the tumble index is the percentage that has remained at plus 1/4 inch. Values greater than 94 percent are generally recommended. 2

6 The fired pellet compression strength was measured with an automated machine according to the ASTM procedure. An average of the 60 pellets crushed is reported along with the percentage that was minus 200 lb. A value of over 500 lb is usually considered acceptable. Pellet porosity was determined by measuring the apparent density in water and the true density with an air pycnometer. The porosity or voids is calculated based on these values. The L TB and reducibility tests were run using the standard ISO equipment. However, the procedures were modified to the laboratory tests developed by HYL to evaluate the suitability of ores for direct-reduction in the HYL process. After reaching 950 C the reducing gas was added at 55 I/min with a composition of 55 percent H 2, 21 percent CO, 14 percent C0 2, and 1 O percent N 2 in the reducibility test. A rate constant "K' was calculated as the slope of the line generated by plotting kt= In (1/1-R) where R is the degree of reduction and t is the time for reduction. A higher value of "K" indicates a better reducibility and a value over 4.0 is desirable. A value for the R 40 or rate of reduction (%/min) at 40 percent reduced was also calculated for each test. The static L TB test used 20 I/min of the same gas composition as above at 500 C. After reduction for 1 hour the pellets were tumbled for 10 minutes at 30 rpm. This material was screened and the percentage plus 6.3 mm and minus 0.5 mm are reported. A value of over 90 percent plus 6.3 mm is usually recommended. DISCUSSION OF TEST RESULTS The results of the test program are presented in the following discussion as two phases of test work. The bench-scale phase covers the evaluation of potential pellet feeds and the pelletizing phase covers the pot-grate tests on the bulk sample. Bench-Scale Tests The three 50-kg iron ore samples were each mixed and representative head samples were removed for detailed chemical analyses. These analyses are presented in Table I which shows that the iron content varies from 65.0 to 68.5 percent. Correspondingly, they contained 1.49 to 5.30 percent combined Si0 2 and Al gangue. Thus, the iron ore fines from Mineral Sales Private, LTD and Ramandburg fines from Bellary Hospet Pvt would both be considered high-grade (less than 2% Si0 2 and Al ) that are suitable for direct-reduction pellets while the Donimalai fines from NMDC are more characteristic of a blast furnace feed material. The Donimalai fines would require grinding and beneficiation to obtain a suitable grade while the others could be used "as is" or upgraded slightly. Ferrous iron analyses ranged from 0.16 to percent indicating all three would contain small amounts of magnetite, but are predominantly 3

7 hematite. The major gangue constituents being Si0 2 and Al are characteristically in a ratio of 1 :1 for all three materials. The minor elements are not excessive except the phosphorous is slightly high in the Donimalai fines. Size analyses conducted on the three samples are given in Tables II, Ill, and IV. Chemical analyses for Fe, Si0 2 and Al were also conducted on each size fraction and are also given in the same tables. Data for the Mineral Sales sample (Table II) indicates about 30 percent of the Si0 2 and Al are in the.finest fraction (500 mesh) and a simple desliming process could be used to make a high-grade concentrate containing under 1.5 percent Si0 2 plus Al The size and chemical analyses for the Donimalai fines (Table Ill) also show the minus 500-mesh fraction to be lower grade, however, the weight percent is small and the grade would not be improved enough by just desliming. The changes in grade by fraction are not significant indicating no major shift in liberation. The Bellay Haspel sample also shows about 30 percent of the gangue is in the minus 500-mesh fraction (Table IV) and could also be upgraded by desliming. However, the "as is" grade is already very good and upgrading to under 1 percent gangue is probably not warranted unless it was to be mixed with a lower grade ore. Grindability Tests. Bond grindability tests were performed on the three small samples and the bulk sample at a 200 mesh-of-grind. The results of these tests are given in Table V and show the work index ranged from 10.7 to These values indicate the ore should not be difficult to grind and can be classified as medium hardness. This data can be used to estimate the grinding mill size and energy requirements for the commercial plant. Beneficiation Tests. The Donimalai (NMDC) sample was subjected to WHIMS and table testing to determine the potential for upgrading. Feed material for these tests was prepared by roll crushing to minus 20 mesh, 48 mesh, 65 mesh and 100 mesh. Results of the single stage WHIMS tests on the 20-mesh feed are presented in Table VI. This data indicates a grade of 66.9 percent Fe and under 3.0 percent Si0 2 plus Al could be produced at the lower intensity, but iron recovery would be under 90 percent. By using a finer feed the same grade can be produced at slightly better recovery, i.e. at 65 mesh a 66.9 percent Fe concentrate was produced with 2 percent better recovery (Table VII). As shown in Table VIII, for the tests with the finest feed (-100 mesh), the best grade that was produced was 67.3 percent Fe and 2.35 percent Si0 2 plus Al However, the iron recovery would be under 80 percent which would not be satisfactory unless the tailings could be blended with a blast furnace feed. Two-stage WHIMS tests with the minus 48-mesh feed were conducted to look at improving recovery. The results are given in Table IX and the treatment flow sheet is also shown. The first stage was run at lower intensity and then the middling and tailing 4

8 were retreated at a higher intensity. By combining the two concentrates an overall iron recovery of 95 percent could be obtained with a 66.5 percent Fe concentrate. However, if concentrate II was recirculated as the middling to Stage I then a 66.9 percent Fe concentrate would be produced at a 94 percent recovery. A table test on the minus 20-mesh feed was also conducted and the results are shown in Table X. This produced a suitable grade concentrate of 67.0 percent Fe but the recovery was low and the middlings were 23 percent of the weight. A circuit combining the gravity concentration (table) and WHIMS was also tested as shown in Table XI. The middling and tailing from the table test was retreated by WHIMS. A combined concentrate containing 66.9 percent Fe was produced at 90 percent recovery. Thus, a gravity WHIMS circuit could be used to produce about the same grade-recovery as the WHIMS alone if this appears to be a more desirable circuit based on economics. A Davis-tube test on the Donimalai ore gave a concentrate containing 69.9 percent Fe and was 4.6 percent of the weight. This indicates that the plant flow sheet should probably include a low-intensity magnetic separator ahead of the WHIMS. Pelletizing Tests The feed material for.the pelletizing tests was received at Coleraine in 53 bags designated as Donimalai ore fines. This material was combined and mixed to provide one 2-ton bulk sample. A head sample of the "as is" ore was obtained for screen and chemical analyses. The results are given in Table XII and indicate that this material was much higher grade than the small bench-scale sample of Donimalai as the Si0 2 plus Al was 0.72 percent compared with 5.30 percent. This material was also finer and slightly softer (10.7 work index versus 12.8). Preparation of the bulk sample for pelletizing was carried out by dry open-circuit grinding to a target size of 65 percent passing 325 mesh. The actual size analysis for the ground pellet feed is given in Table XIII and shows a grind of 63.6 percent passing 325 mesh was attained with a Blaine of 1595 cm 2 /g. This surface area is lower for that grind than most pellet feeds since there was not a lot of natural fines in the feed to the mill. Size and chemical analyses for the five additives used in the pelletizing test program are presented in Table XIV. The coke breeze and fluxes were dry ground to a nominal minus 100 mesh while the clay and bentonite were obtained as fine materials. The local clay was chosen as an additive to provide additional gangue in the ore since the bulk sample it was expected to contain about 1.5 percent Si0 2 plus Al This clay had a Si0 2 to Al ratio of 2 which was similar to the ore. All of the other additives were also obtained by CRL from USA sources since potential raw materials were not shipped from India. 5

9 The palletizing tests were conducted in the pot-grate based on design data provided by Davy Dravo for the straight-grate firing cycle. A description of the process conditions is shown in Table XV and gives the time, temperature, and pressure drop for each zone. The total machine would contain 58 windboxes and a 12-inch bed of green balls would be placed on top of a 4-inch hearth layer. The initial test was with ore containing 1.0 percent clay to give about 1.5 percent Si0 2 plus Al in the ore. This also increased the Blaine in the pellet feed by about 100 cm 2 /g. Other additives in the mix were based on the weight of dry ore/clay. An addition of 1.0 percent bentonite, 1.0 percent coke, and 3.5 percent dolomite made up the pellet feed for Test G-1. Using the process cycle shown on Table XV and a firing temperature of 2336 F resulted in very weak (399 lb) and porous looking pellets that contained magnetic cores. The reversion to magnetite caused by very high bed temperatures indicates the fuel was too high. Therefore, in Test G-2 the coke was reduced to 0.5 percent and the peak firing temperature was reduced to 2300 F. Since the green balls in Test G-1 also had drop and compression strengths that were too high, the bentonite addition was lowered to 0.5 percent for Test G-2. This level produced good green-ball quality and was used in the remaining tests. A summary of the test conditions and results for these tests is given in Table XVI and shows good quality fired pellets were produced in Test G-2 at a production rate of 2.07 MT/ff/D. Fired pellet compression strength was 781 lb and the tumble index was 96.0 percent plus 1/4 inch. The dolomite addition was aimed at producing a pellet containing 0.8 percent MgO and a basicity (B/A) of 1.0 to achieve good metallurgical properties. Based on the reducibility and L TB test results it can be seen that high quality pellets were produced. The 950 F HYL reduction test gave a K x 10 2 of 6.5 which is well above the 4.0 normally specified. In Test G-3 the ore/clay mixture was again used and the dolomite addition was reduced from 3.5 to 2.5 percent to investigate the effect of MgO level on pellet quality. This gave an MgO level of 0.6 percent and also lowered the B/A to 0.7. The results of this test (Table XVI) show a lower compression strength of 633 lb and also a slightly lower reducibility K x 10 2 of 6.2. L TB results were also lower and were about at the minimum level of 88 percent plus 6.3 mm specified by HYL. The pellet feed for Test G-4 was the ore/clay mix (1.5% Si0 2 + Al ) with a 1.0 percent limestone addition while G-5 used the "as is" ore with 1.0 percent limestone. Both tests produced excellent quality pellets. The physical quality with limestone was better than with dolomite and the metallurgical properties were slightly better for the L TB and about the same for the reducibility. Thus, either silica level would produce suitable quality pellets using only a 1.0 percent limestone addition instead of dolomite. The "as is" low-silica ore was also used in Test G-6 with a 2.5 percent dolomite addition and no limestone. This was the maximum level of dolomite that would be practical without producing too high basicity. At this level of dolomite the pellets had an MgO content of 0.6 percent and a B/A of The fired pellets from this test had good 6

10 compression strength (733 lb) and a tumble index of 95.4 percent. However, the reducibility was about 30 percent lower than in the other tests. A value for K of 4.4 was attained in the HYL Flg 50 test compared with 6.2 in Test G-3 using 2.5 percent dolomite and the higher silica feed. Thus, with the low-silica ore the high levels of MgO would not be desirable. In Test G-7 the pellet feed had 1.0 percent limestone and 1.0 percent dolomite added to the higher silica ore/clay mix. These pellets were fired with the standard cycle and 0.5 percent coke breeze. The product from this test had excellent quality as shown by the results in Table XVI. The compression strength was 782 lb with a tumble index of 96.6 percent. Reducibility of these pellets was the highest produced in any of the tests with a K value of 7.1. Thus, it appears that compared with Test G-4 where only limestone was added that a small amount of MgO is beneficial in improving the reduction characteristics. CONCLUSIONS The test data developed in this program should provide the design information required by Davy Dravo for the Grasim feasibility study. An evaluation of three ore samples indicates that these materials are either suitable for direct-reduction pellets or could be upgraded to provide the desired grade. If the lower grade ore from NMDC Dionimalai is to be used it would require a beneficiation plant beyond the simple desliming plant that would suffice for the other ores. It appears that a WHIMS circuit would be suitable for concentrating this material, but it would be difficult to attain less than 3.0 percent Si0 2 plus Al with a good iron recovery of over 90 percent. The grindability of the ores tested in this program indicate grinding to palletizing feed should not require excessive energy. The Bond work index values of 10.7 to 15.4 can be used to design the grinding circuit and estimate power requirements depending on the ore that will be used in the commercial plant. Palletizing tests were performed with limestone and dolomite additives to look at the effect of chemistry on pellet quality. Two levels of Si0 2 plus Al in the ore were tested. In general, a high quality pellet was produced at both the nominal 1.1 and 2.0 percent levels of Si0 2 plus Al in the final pellet. Physical quality was very good regardless of the chemistry, but the addition of limestone appears to give the best physical strength. Total basicity varied from 0.37 to 1.26 with the MgO content varying from 0.1 to 0.8 percent. The intermediate level of B/A gave the lowest L TB while the lowsilica pellets with a high basicity had the lowest reducibility. 7

11 Production levels in the range of 2.0 to 2.1 MT/ft2/D resulted from the processing cycle recommended by Dravo. This was achieved by using 0.5 percent solid fuel (0.43% carbon) to provide some of the extra energy required for fluxed pellets while still maintaining a high production rate. In general, the results of this program demonstrated a high quality pellet suitable for direct-reduction feed was produced with the Donimalai ore at a satisfactory production level. 8

12 Table I DRAVO GRASIM INDIA PROJECT Chemical Analyses of Iron-Ore Samples for Bench-Scale Testing Percent Sample ~ Fe ff Si02 Al203 Cao!:!gQ_ Na20 K20 p Mineral Sales Private, LTD (ROM Fines) NMDC Donimalai Q (Fines) Bellary Hospet Pvt (Ramandburg Fines)

13 Table II DRAVO GRASIM INDIA PROJECT Size and Chemical Analyses for ROM Iron Ore Mineral Sales Private LTD Wt% 3/8" /4" 5.5 %Cum O/o % % % Passing Fe Dist SiO, Dist % % Al20, Dist Mesh Total Head Assay

14 Table Ill DRAVO GRASIM INDIA PROJECT Size and Chemical Analyses for Donimalai Iron Ore (NMDC) %Cum % % % % % % Size Wt% Passing BL Dist Si02 Dist Al20a Dist 3/8" /16" /4" Mesh Total Head Assay

15 Table IV DRAVO GRASIM INDIA PROJECT Size and Chemical Analyses for Iron Ore Fines Bellary Hospet PVT. - Ramandburg %Cum O/o O/o % % % O/o Wt.% Passing Fe Dist Si02 Dist ~Qi Dist 3/8" /4" Mesh Total Head Assay

16 Table V GRASIM PROJECT - BOND GRINDABILITY Sample Work Index (200 Ml Mineral Sales Private, LTD (ROM Fines) 15.4 NMDC Donimalai (100-lb Sample) 12.8 NMDC Donimalai (Pilot-Plant Sample) 10.7 Bellary Hospet Pvt. Ramandburg Fines 11.9

17 Table VI Dravo Grasim India Project Results of WHIMS Tests on 20-Mesh NMCD Iron Ore Fines Fe Recovery, Product Wt.% Fe.% Si02. % 61,Q,. % % Test No. 1-1 o Amps Concentrate Middling Tailing Total Test No Amps Concentrate Middling Tailing Total Test No Amps Concentrate Middling Tailing Total

18 Table VII Dravo Grasim India Project Results of WHIMS Tests on 65-Me.sh NMCD Iron Ore Fines Product Wt,% Fe.% Si02. % 61,01. % Fe Recovery, % Test No Amps Concentrate Middling Tailing Total Test No Amps Concentrate Middling Tailing Total

19 Table VIII Dravo Grasim India Project Results of WHIMS Tests on 100-Mesh NMCD Iron Ore Fines Fe Recovery, Product Wt,% Fe.% Si02. % ~o,, % % Test 7-10 Amps Concentrate Middling Tailing Total Test 8-20 Amps Concentrate Middling Tailing Total

20 Table IX DRAVO GRASIM INDIA PROJECT Results of Two-Stage WHIMS Tests on Minus 48 Mesh Donimalai Fines Product Wt, % Fe, % Dist, % Si02, % Dist,, % Al203, % Dist, % Concentrate I 83.8 Concentrate II 9.2 Tailing 7.0 Total CI + CI! 93.0 Cone. - Cale* * Calculated closed-circuit recovery based on recirculating Cone II as middling. Flow Sheet I Minus 48-Hesh Feed! WHIMS (10 Am s) CI MI TI CI! MII r I Tails TII {

21 Table X DRAVO GRASIM INDIA PROJECT Results of Table Test on Minus 20-Mesh Donimalai Fines Product Wt, % Fe, % Dist, % Si02, % Dist, % Al203, % Dist, % Concentrate Middling Tailing Total

22 Table XI DRAVO GRASIM INDIA PROJECT Results of Table/WHIMS Test on Minus 20-Mesh Donimalai Fines Product Wt, % Fe, % Dist, % Si02, % Dist, % Al203, % Dist, % Cone I - Table Cone II - WHIMS Middling II Tailing II Total Cl + CII Flow Sheet I Minus 20-Mesh Feed CI I Table I f I TI MI '--~---' r- CII MII TII

23 Table XII DRAVO GRASIM INDIA PROJECT Size and Chemical Analyses for Donimalai Iron Ore (NMDC) Bulk 2-Ton Sa,mple Size 3/8 Inch 5/16 Inch 1/4 Inch 4 Mesh 6 Mesh 8 Mesh 10 Mesh 14 Mesh 20 Mesh 28 Mesh 35 Mesh 48 Mesh 65 Mesh 100 Mesh 150 Mesh 200 Mesh 270 Mesh 325 Mesh 400 Mesh 500 Mesh -500 Mesh Total Wt,% % Cum Passing Head Assay FeT Si0 2 Al cao MgO 69.1% 0.47% 0.25% 0.05% 0.06%

24 Table XIII DRAVO GRASIM INDIA PROJECT Size Analysis of Ground Donimalai Pellet Feed Size. Mesh Wt.% Cum% Passing Total Blaine 1595 cm 2 /g

25 Table XIV DRAVO GRASIM INDIA PROJECT Size and Chemical Analyses for Palletizing Additives Dolomite Coke Breeze Limestone Cum% Cum% Cum% Size. mesh Wt,% Passing Wt.% Passing Wt,% Passing Total Chemistry Dolomite Limestone Clay Bentonite Coke Breeze Fer,% Si0 2, % Al 2 0 3, % Cao,% MgO,% LOI,% FC,% 86.4

26 Table XV DRAVO GRASIM INDIA PROJECT Pot-Grate Test Firing Cycle Process Gas Zone Wind boxes L'lP, in..'.'._f_ Time. min Updraft Drying Downdraft Drying Preheat Firing * Recuperation Updraft Cooling Total * Firing 4-7 was 2336 F for Test No. 1. Note: Green-ball density'was 134 lb/ft 3.

27 Table XVI DRAVO GRASIM INDIA PROJECT Summary of Pot-Grate Palletizing Test Data G-1 G-2 G-3 G-4 G-5 G-6 G-7 Green Balls (-1/2 +7/16") Bentonite, % Coke,% l Limestone, % ~ Dolomite,% Moisture,% Drops, No Compression, Dry, lb Wet, lb Processing Rate, MT/ft 2 /day Bed Depth, in Hearth Layer, in Ignition Temp, F Grate +6", Peak F Grate + 1 O", Peak F Grate + 14", Peak F Product Compression, lb Top Bottom Average % Minus 200 Pounds Before Tumble, +1/4", % After Tumble, + 1/4, % FeT, % FeO, % Si0 2, % Al 2 0 3, % Cao,% MgO,% B/A LTB +6.3 mm,% mm,% R 40, %/min HYLR 950 K x '..! Porosity,% Tests 5 and 6 are with low Si0 2 ore.