PILOT PLANT TESTING METHODSBy B.P.RAVI, D.O.D.O., I.B.M., Bangalore

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1. I N T R O D U C T I O N

The mineral processing industry is a demanding and risky industry, from economic and time points of view. In view of the high risks and time requirements, it is advisable to get the ore test thoroughly at laboratory and pilot scale levels. Proper development and interpretation of test data and the coherent picture of metallurgical response with size and plant for the deposit are basic necessities for a mineral project development.

A mineral project development work has to pass through about 10 diverse stages. The timely growth of mineral processing project indicates that flow-sheet development and preliminary techno-economic feasibility report, consuming about 30% of project start-up time. (Ref. Fig.1)

The test work is a continuous on going process and is carried out in stages mentioned below:

1. Ore characterization, amenability tests – at exploratory stage by prospecting team.

2. Preliminary bench scale open cycle ore dressing tests – for diverse indicative flow-sheet development on different ore types.

3. Confirmatory, locked bulk bench scale tests or bulk semi-continuous pilot plant scale tests and continuous pilot scale tests on bulk samples – for flow-sheet modification, confirmation, engineering, process, marketing and data generation.

4. Preliminary tech-economic feasibility study.

5. Semi commercial small-scale continuous pilot plant operation at site – for data generation on environment, demand for feasibility (definitive).

6. Routine scale down bench scale tests for control and optimization of plant (plant auditing studies).

The objective of this paper is to study the various aspects of continuous pilot scale, semi-continuous pilot scale and lab scale tests simulating plant conditions that is normally practiced during flow-sheet development and project evaluation stage.

2. NECESSITY OF PILOT SCALE AND BULK LOCKED BENCH SCALE TESTING

The bulk locked bench scale testing and pilot scale testing is necessary for flow-sheet confirmation of flow sheet due to the following advantages:

1. Flow sheet indicated in a bench scale test report is confirmed in a pilot plant and modified to produce better results like middling recirculation.

2. Generates process and engineering data for basic design of commercial operation and products for market and environmental study.

3. Increases process confidence by operator training demonstrates process on a continuous basis for investors.

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4. Commercial plant conditions are nearly simulated viz., by using reclaimed water, recirculating middling and preliminary guidelines for establishing tail pond system.

5. Data is obtained on large quantity of bulk sample even for trace valuable recovery and indicates sensitive areas for commercial utilisation.

6. Data furnishes models for given ore types and indicates sensitive areas for commercial operation.

7. Testing charges are just 0.1% of the total capital investment and averts probable future process frustrations like insurance.

Certain limitations of pilot plant testing are listed below:

1. Pilot plant testing needs more time, money, and multi-disciplinary teamwork right from sample collection to plant stabilization.

2. Data can be obtained from mismatched small machines.

3. Data obtained by process conscious skilled engineers. Normally results of failure runs, frequency of failure runs and their cause, down time data, sampling, analytical and ore characterization procedures are not furnished.

4. Capacity of pilot plant testing depends on mineral content, size, concentration method, and degree of heterogeneity of sample rather than size of deposit and capacity of further plant.

5. Sometimes pilot plant testing is done away from site.

Entrepreneurs avert sometimes pilot plant testing when,

Ore body is small, uniform and ore is sweet. Bench scale flow sheet is simple, feasible and efficiency of ancillary operations do not affect project metallurgy e.g. gravity and magnetic concentration circuits – of BMQ/HGMS of clay.

Ore is tested in a continuous commercial plant as in case of expanding the capacity of existing plant.

Company is ready to absorb risks and wish to make quick profit during boom period (as in some custom plants) and equipment supplier furnishes the process guarantee.

High unit capacity gravity circuits are involved, where; semi-commercial pilot plants are favoured, as they become a part of future commercial plant.

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3. DATA NEEDED FOR BULK LOCKED BENCH SCALE TESTING AND CONTINUOUS PILOT SCALE TESTING

The following data is a sine-qua-none before proceeding for pilot scale testing.

The following Table 1 denotes, data to be provided at the time of pilot plant testing.

Table - 1

DATA NEEDED FOR PILOT PLANT TESTING

SL.NO

.DATA PARTICULARS

1 SamplesRequisite quantity of samples (ore and water*) as per Gy’s formula and process requirement should be furnished along with method of sampling, duration, location of deposit, technical amenability plan of deposit.

2 Literature

Test reports of bench scale tests on above sample, literature, if any, on similar plant practice, revolutionary technology process/machine data* objectives of study and scope of test work should be furnished before sending samples. Also, diverse market specifications, rates, nature and markets, situations (geo-eco-political) should be furnished before testing.

3 DepositLocation, geography, genesis and mineralogy of deposit have to be furnished.

4 Personnel

The experience, bio-data of multi disciplinary joint teams comprising of geologist, mining engineer, chemical analyst, mineralogist, ore dressing scientist, plant metallurgist, mineral economist should be decided before test work.

5 CompanyCompany profile, philosophy and professional experience in the field has to be furnished.

4. UNIT OPERATION IN PILOT PLANT TESTING

The following are the unit operations involved in pilot plant testing:

Blending/mixing and sampling

Conventional crushing and screening tests.

Conventional open circuit rod milling and ball mill classifier closed circuit grinding.

Bulk semi-continuous gravity concentration involving heavy media, cyclones, locked spirals concentration tests and locked tabling tests.

Bench scale locked wet LIMS and WHIMS

Continuous conventional flotation circuits (open and locked).- 4 -

Bond’s crushability test, Bond’s rod mill grindability test, Bond’s abrasion test*, Bond’s ball mill grindability test, Denver grindability test, laboratory thickening test, leaf filter tests simulating disc/drum filters, laboratory Larox pressure filtration test.

Other tests if needed by the party viz., leaching/ion exchange test, aggregate testing, sintering, pelletisation and briquetting test, etc.

4.1. BLENDING/MIXING AND SAMPLING :

In a pilot plant blending/mixing and sampling are drawn manually. However, at crushing stage, facility, has been provided to draw samples continuously from falling stream by Snyder’s sampler. The types of samples drawn are tested as below:

Coning and quartering, riffle sampling of dry solids by Shovels.

Mixing can be done by recirculating material from bins/sumps using feeder/valves – bucket elevator/pumps etc.

Pulp stream sampling by using cutter scoops/buckets

(a) Instaneous time samples for random metallurgical balance (1 minute time samples)

(b) Incremental time samples for metallurgical balance of runs (1-minute time samples at regular intervals).

(c) Random lip and cut samples for process study.

(d) Bulk time samples for sub-tests, market survey and project metallurgy (4-8 hrs)

The details of sampling have been discussed earlier.

4.1. CONVENTIONAL CRUSHING AND SCREENING TESTS

The objective is to produce desired size range of crushed and screened aggregate and the circuit determines approximate energy/ton of product produced. It is normally used in:

Preparing feed for subsequent comminution circuit or concentration circuit e.g. jigging.

Preparing close sized range products e.g. aggregates of limestone or iron ore.

As a pre-concentration device eliminating/reducing two diverse phases, based on size and shape e.g.

(a) removal of clayey material from limestone

(b) Separation of needle shaped Wollustonite from cubical calcite.

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The circuit comprises of double deck screening, followed by top deck over-size fed to primary jaw crusher. Jaw crusher products and double deck screen bottom deck oversize is crushed in standard cone crusher. The cone crusher product is recirculated back to D.D. screen. Crushing and screening circuit is capable of generating products from 600-mm double deck to 10-mm size range products on a continuous basis. (Ref. Fig.2).

4.2. CONVENTIONAL GRINDING CIRCUIT

The conventional grinding circuit comprises of either an open circuit rod mill or closed ball mill classifier circuit or rod mill. Ball mill classifier circuit. The objective of grinding circuit is to produce ground product of specified size band, (furnishing % retained top size, d80 microns, % passing bottom size), pulp density (% S), at a specified throughput on a continuous basis and energy/ton or WIo,

WIo = Em (Pg – Po) x Ef x Cf

Q 10 _ 10 P80 F80

Where WIo = Operating Work Index – KWh/ton

Em = Mechanical Efficiency Pg = Gross Power

Po = no load power Ef = Electrical Efficiency

Cf = Mill Correction factor Q = Throughput in tons/hour

P80 = 80% passing product size F80 = 80% passing feed size

The mill is fed by a 300-mm wide belt feeder. The length of mill, nature and amount of load can be varied. Either a 4”/2” hydrocyclone or 3 spiral classifier can be used in case of closed circuit grinding. The variables like feed rate, feed size, load weight and composition, dilution ratio, classifier parameters can be varied to achieve the objectives. Normally rod mills are employed gravity circuit i.e. tables, spiral or magnetic concentration circuits viz. WLIMS or WHIMS. Ball mill and cyclone/spiral classifier circuits are employed when finer feeds are needed for the subsequent concentration process viz. flotation etc.

A small ball rod tube mill, spiral classifier or hydro-cyclone may be used for regrinding minus 10 mesh size feed/middling products in case of necessity of regrinding circuits. The relationship between gross energy in put, load and size of products enables the estimation for determining operative work index. The type of grinding circuit and through put chosen depends on size band of products, subsequent concentration method stream constraints and % abundance of minerals to be separated etc. The M.O.G. is normally maintained by optimizing ore configuration and weight of load, dilution, length of mill, adjusting classifier parameters and some time feed size. The water additions are regulated by flowrators. Water and feed rate, % S are recorded. Composite incremental time sampling of incoming outgoing products are made manually at incremental time of 15’ to 30’ using scoops etc. Also one time samples are collected at the end of run and %S, size configuration, pulp density are determined from the one time samples drawn.

Fixation of grind consumes time to extent of 30% of total time and quantum of sample. (Ref. Fig.3).

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4.3. GRAVITY CONCENTRATION CIRCUIT

The gravity circuit facility normally available in a pilot plant are jigs, heavy media cyclone, DWP, Spirals, Richert tray test assembly, tables, and Mozley’s multi gravity separator in decreasing order of feed size granulometry and decreasing order of throughput. Before feeding gravity circuit, the prepared feed is subjected to diagnostic mineralogy, size analysis, liberation and Heavy Liquid Separation to evaluate the efficiency and normally no scale up factor is needed to determine the throughout. We shall be limiting ourselves to Humphrey’s spiral concentration test tabling and cycloning test. Other process and equipment may be discussed in the subsequent lecture.

4.3.1. Spiral Testing :

The feed sample is stage crushed to desired M.O.G.. (20 to 40 mesh) either in a batches is lab roll crusher or on continuous basis in a rod mill (open circuit). The ground sample is fed to sump (with agitator). The pulp from sump is pumped to variable apex desliming cyclone by sand pumps at 15 to 20 GPM and desliming cyclone O/F is adjusted to 5 to 8 GPM (as wash water), the desliming cyclone U/F at 25-40% is fed to 5 turn 220 mm, medium profile spiral at a rate of 0.5 to 1.0 tph. Initially, batch tests are carried out with 5 ton samples by re-mixing heavies and lighter fractions varying splitter positions, %S, wash water. The 1’ time samples and bulk samples are collected (15 to 30’). Samples are evaluated for assay, size analysis, %S. Once parameters are fixed in batch, closed circuit spiraling, continuous test using a number of spirals may be necessary to get actual metallurgical balance. The other operating parameter viz., throughput, rpm, (PSI), pressure, amperage etc., are noted (Ref. Fig.4.)

4.3.2. TABLING :

The sample is stage crushed to desired size (35 to 100 mesh) and is fed to Wilfley table at 0.25 to 0.5 TPH (20 to 40% S). Like spiraling, initially batch tests are carried out on 5 ton samples, re-mixing table products and re-feeding. Parameters like size, riffle deck type, tilt, wash water rate, %S, splitter positions are varied. Time samples and bulk samples are collected and evaluated for assay, size analysis. Subsequent locked clean/scavenger operations may be carried out on bulk samples collected. Once parameters are fixed in batch test, closed circuit tabling, tests are done on continuous basis using a number of tables to obtain actual metallurgical results.

4.3.3. CYCLONING TESTS :

Batch closed circuit cyclone test may be carried out by pumping slurry to cyclone at set pressure, flow rate and P.D. (%S), parameters like feed size, P.D. Pressure, capacity of pump and rpm and cyclone geometry are varied. Time samples and bulk time samples are collected for evaluation and subsequent tests (Ref. Fig.5).

A schematic flowsheet of gravity concentration circuit employing jigs and tables in shown in fig. 6.

A schematic flowsheet of beneficiating iron ore fines from reject dumps employing scrubbing, classification and jigging is shown in Fig.7. Fig.8 and Fig.9 depict the material and metallurgical balance of the above flowsheet.

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4.4. MAGNETIC CONCENTRATION CIRCUIT

The magnetic concentration circuit normally available in a pilot plant are wet LIMS drum separator, wet high intensity magnetic separator and HGMS separator. Like gravity circuit, feed preparation is vital and no scale-up factor is needed to determine retention time/throughput. Locked bench scale tests are carried out using wet LIMS or dry MIMS simulating plant conditions.

A schematic flowsheet for WLIMS and WHIMS is shown in Fig.10 and the data of the above studies is shown in Table 3.

4.5. FLOTATION CONCENTRATION CIRCUIT

Before going for pilot plant testing, we need to undertake bench scale beneficiation studies to obtain the required parameters like, grind, reagent consumption, flotation time P.D. etc. The conventional flotation facilities normally available in a pilot plant are conditioners, reagent feeders, flotation cell batteries, reagent pumps, slurry pumps of varying volumes/capacities.

Before feeding the pulp (classifier over flow) to flotation circuit, either an open or locked bench scale tests are carried out along with diagnostic ore characterizing amenability tests to verify bench scale results and evaluate the efficiency of feed preparation. As a thumb rule, a scale-up factor 2-3 is used to determine retention time during flotation.

The cell peripheral speed (fpm) is almost kept similar to that of lab cells. The throughput depends upon the capacity of cell, percentage mineral to be floated, slurry volumetric flow-rate of slurry, froth factor and pump capacity. The pilot plant may be equipped with required flotation batteries (6 each) of suitable capacities.

The flotation circuit is arranged as per bench scale flow sheet. During preliminary runs, open cycle tests at every stage is carried out and machine parameters, percentage solid, launder water, retention time, flotation stages, reagent dosage are varied (machine, circuits reagents). Incremental time and bulk samples are collected and are evaluated for assay, size, %S, Sp.Gr. throughput, flow-rate and diagnostic mineralogical studies. The bulk samples are reserved for thickening, filtration and marketing studies. Tests are also carried out using reclaimed water and effluents are analyzed and the actual metallurgical balance is prepared. (Ref. Fig. 11 to 13)

4.6. Ancillary tests:

Bench scale lock tests are carried out on scale down pilot plant conditions to evaluate the pilot plant operation (using reclaimed water). Other bench scale tests viz. heavy media bucket tests for HMS, Jigs, agitational leaching in stainless Steel jars, leaching column tests, resin adsorption tests, batch scrubbing tests using mixer, column flotation tests may be carried in a locked manner. These topics has already been discussed earlier.

The particulars of the test data that are studied during column flotation test is shown in Table 5 and Fig.14 & 15.

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4.7. Simulatory Lab Tests

The tests are carried out on samples simulating plant conditions to evaluate data for conceptual design. They are as follows:

(i) Bond’s work index viz. Crushability, rod mill and ball mill grindability.(ii) Unit thickening area for thickness(iii) Specific filtration rate.(iv) Denver grindability for filters hardness of sample.(v) Bulk density, density, and angle of repose for determining the capacity for

ore bins.

4.7.1. Evaluation of bulk density, angle of repose, density etc :

These are determined using one cubic meter container, measuring angles of conical heaps, pycnometer, as per standard ISI procedures.

4.7.2 Bonds Work Index: It is determined as per the procedure mentioned in Fred C. Bond method.

4.7.2.1.Crushability:

Crushability test is done by using twin pendulum impactor of 4 square inch cross section on –3+2” material by simultaneous impact of pendulum for various equal angles. The angle which crushes the specimen () and thickness (t) of specimen in inches, density (D) are recorded. The test is carried out for 20 specimens. Work index is calculated by following formula:

Wic = 2.59 x 82 x (1 – cos ) D x t

4.7.2.2. Bond’s rod mill work index :

It is determined by using 12” X 24” rod mill, 8 nos. rods (1.75” and 1.5” dia) weighing 33,360 gms) on stage crushed, - ½”, 1250 ml material for producing 100% circulating load (using test sieve 10 to 150 mesh). The Bonds’ rod mill work index is calculated by the formula as below.

The feed and products (which produce 100% CL at constant Grp and no. of rotations) are sieved.

6.2.WIR =

Pi0.23 x grp0.625 x 1 1 P80 F80

Pi = aperture of test sieve opening

Grp = grindability (gms/rev) at equilibrium cycle.

P80 = 80% passing product size in microns

F80 = 80% Feed size (-1/2”) in microns.

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4.7.2.3. Bonds’ ball mill work index

It is determined using 12” x 12” ball mill of 70 rpm with 285 steel balls of 1.5”, 1.25”, 1.0”, 0.75” and 0.5” dia weighing 20, 125 gm on –6 mesh stage crushed, 700 ml sample for producing constant 250% circulating load on test sieve preferably 150 mesh (28 mesh to 325 mesh). The products (which produces constant 250% CL constant, number of revolutions and gbp) and fresh feed are subjected to sieve analysis to determine P80 and F80 size.

The Bonds’ ball mill work index is calculated by the following equation. It is always advisable to carry out WI values at different particle sizes near to M.O.G. (80% passing values to have a mean WI value with size.

WiB = . 4.45 . Pi0.23 x Gbp0.82 x 1 _ . 1 .

P80 F80

Pi = aperture of test sieve opening

Gbp = grindability (gm/rev) at equilibrium cycle

P80 = 80% passing product size in microns

F80 = 80% passing feed size in microns

4.7.2.4.Thickening tests:

Batch settling tests on 2 ltr fresh pulps using 2 ltr measuring cylinder are carried out with and without addition of flocculent. The mud line height with reference to time is noted, for each minute. Ho and Hu is marked after 19 hrs. The nature of pulp surface, floc size, super natant water quality are also recorded. The tangent of H-t curve at compression point intercepting Hu time axis curve will furnish tu. The unit thickener area without safety factor is calculated by Kynch equation as below :

UA = tu .CoHo

tu = Ultimate time in days (from curve)

Co = initial concentration (t.m3)

Ho = initial height in mtrs.

4.7.2.5.Vacuum leaf filter test

Filter productivity = Fv = Cake wt. (gms) x 10 -6 x 3600 0.0093 x Cycle time in secs.

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4.7.2.6.Pressure filter test

Similarly pressure filter tests are carried out using Larox 50 cm2 filter at 4 bar pressure varying cloth and %S.

Filter productivity = Fp = Cake wt. (gms) x 10 -6 x 3600 0.0050 x Cycle time in secs.

4.7.2.7.Abrasion test :

3” x 1” x 10.25” of 500 Brinnel hardness paddle fitted in 4.5” dia. rotor, rotating at 632 rpm in a 12” drum Dia. x 4.5” long rotating at 70 rpm. 400g (- ¾ + ½) samples ground for 15 minutes. Wt loss is Ai. KW/t Liners =K ( Ai - 0.015 )0.3 K= 0.35 for rod mill liners, 0.026 for ball mill liners KW/t Balls =K1 ( Ai - 0.015 )0.33 K1 = 0.35

KW/t Rods =K2 ( Ai - 0.020 )0.22 K2 = 0.35 KW/t crushers = (Ai + 0.22) / 11

5. STAGES IN PILOT PLANT TESTING

Bulk locked lab tests and continuous pilot plant tests are normally carried out in 3 stages:

5.1. Break in operations (Preliminary trials):

In this period the plant is run normally for a brief period (8 hours max). The mesh of grind will be fixed. The concentration and ancillary units are arranged and checked without load. Bugs are ironed out and circuit is fed with ground pulp to make operators familiarize with ore. Sampling procedures are formulated for collecting bulk, incremental time, lip and random samples.

5.2. Operations for optimization :

The plant is operated to optimize parameters for each unit operation. The effect of parameters, circuit configuration on product metallurgy is determined. Regression models may also be prepared. This is the important and longest period during a pilot plant testing where data is recorded. The runs will be restricted to a minimum of 12 hours per trial.

- 11 -5.3. Continuous operation

The plant is run on continuous basis and reclaim water will be circulated. Lab tests are performed on ground ore sample under study on scale down pilot plant condition for control operations. Actual and calculated metallurgical balances are compared. The bulk sample products obtained may be sent for other simulatory test work, namely thickening and filtration tests, etc. and the products may also be sent for initial market survey. The critical/sensitive/grey areas are identified. Empirical models are developed. Process is guaranteed in terms of process stability by statistical terms, namely standard deviation and confidence levels.

Whenever, facilities are not available to carrying out continuous runs, using reclaimed water, locked laboratory cycle tests are performed under scale down plant conditions using the reclaimed water.

The utility of pilot plant data is shown in table - 2.

6. PILOT PLANT TEST REPORTS

The pilot plant ore dressing test reports containing the data is furnished below:

1. Title page and principle team members involved in the pilot plant test work.

2. Index

3. Abstract: An executive summary of the work done indicating the chemistry, Mineralogy and ore characterization along with the brief data of test results and conclusions.

4. Introduction: Data about the origin of the sample, previous history of test data, objective and scope of test work and specifications are furnished.

5. Experimental work: The details of the test work done are described and results are shown.

6. Observation Discussions, conclusions and recommendations: The observations during the trials, the experimental results are discussed and conclusions are drawn and recommendations are made.

7. Acknowledgments

8. Tables of Test data

9. Figures showing the metallurgical balances, flowsheet and other experimental data.

10. Details regarding the scale-up factors, safety factors and local factors regarding the engineering and process problems are shown.

11. Annexure of test data of break-in-operation runs and other spoiled runs may be incorporated, if desired by the party.

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7. C A S E S T U D I E S

7.1. Case study of wollastonite beneficiation

A case study furnishing the salient features of pilot plant data, market specifications, rates of concentrates, reserves, span of project, capacity of project, scale-up safety, efficiency and local factors are furnished. A preliminary equipment sizing for 100 tpd mineral processing plant employing crushing, screening, grinding, flotation, magnetic separation, thickening and filtration is presented. The metallurgical, energy, water balances and the man power data is also furnished. The capital costs and operating costs are estimated by factored ratio/order of magnitude method. The profitability is expressed in terms of rate of return after deducting taxes, royalty, interest on capital and other over-heads. The flowsheet of 100 tpd wollastonite ore processing plant denotes in a nutshell the practical utility of pilot plant testing. (Ref. Fig. 13)

7.2. Case study of Rock Phosphate beneficiation

A case study of conforming the process developed by Lakefield Research, Canada by employing a specific reagents for rock phosphate from Lalitpur, UP for M/s UPSMDC is discussed below.

The process is highly effective due to a primary grind of minus 200 mesh, regrind of first cleaner phosphate float to minus 400 mesh, high energy thick pulp conditioning with specific amphoteric collectors consisting of an emulsion of anionic fatty acid collector (48% Oleic, 35% Linolic, 16% others) and cationic modifed fatty amine collector (Lila float OS100) with kerosene in proportion of 5:3:2 and a specific depressants (an emulsion of sodium ortho silicate, MgSO4 and Na2SO3 in 92:4:4 proportion. A concentrate assaying 36% P2O5 was produced with 92% P2O5 recovery. (Ref Fig 6 and 7). The sizing and order of magnitude costs for the above project is given below.

Capacity (tpy of Conc.) 2, 50, 000 1, 00,000Span (years) 10 25Throughput (tpd) 3, 000 1,200Mining Capital Cost ($) 6, 516, 000 5, 181, 300Concentrator Capital Cost ($) 13, 985, 348 8, 779, 800Others ($) 700, 000 424, 000Total Project Cost ($) 21, 201, 348 14, 385, 100

7.3. Case study of Upgrading Iron Ore Fines

For upgrading an iron ore fines reject fines of Goa to reduce the ecological problem of dumping the mine reject a process flow sheet was developed. The process flowsheet, material and metallurgical balances are shown in Fig 7,8,9 respectively. The details of test data studies during the investigation is summarised in Table 4. The above study yielded a composite marketable iron ore fine concentrate assaying 63.5% Fe at 81% iron recovery (Wt.% yield 79.2) from sub grade iron ore of 61.62% Fe. The process utilises

about 80% of the sub grade dumps mitigating the problem of disposal of the sub grade fine iron ores of Goa region, conserving the mineral and additional revenue is generated.

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7.4. Case study of improving the grinding circuit throughput

M/s Hindustan Zinc Limited is operating a 1000 tpd Lead-zinc concentrator at Zawar treating the ore from Balaria. The grinding circuit comprises of two overflow 10X16 feet ball mills with 750hp motor in closed circuit with two D-15 Kerrbs cyclones (ref Fig 16). It was decided by the party to enhance the throughput maintaining the grind. IBM team visited the site and collected samples and carried out work index determination. It was found that Wi (Ball mill) and Wi (rod mill) was 6.24 and 10.1 respectively. The efficiency of the circuit was 71% only. The overseas plant data treating similar ore, the supplier catalogue data indicated that there is a scope for improving the throughput. Without any modifications, maintaining ball charge and maintaining the cyclone parameters, it was possible to rise the tonnage from 40 tph to 48 tph enhancing the productivity by 20%. It was also found that by replacing the hydrocyclone, modifying the launders and pump parameters, the throughput could be increased to the maximum of 50-55 tph (25-40% increased production). The above pilot scale and in plant studies enhanced the profitability of the Balaria circuit by reducing the grinding cost.

7.5. Case study of flow sheet development of Kudremukh Iron Ore

Based on the detailed tests on drill core exploration samples it was found that a high concentrate grade could be obtained by close circuit autogenous grinding and WLIMS. The pilot plant operation comprising of close circuit wet autogenous grind followed by LIMS and spiral separation the tests on different ore types from different parts of the ore body yielded a blast furnace grade concentrate at minus 10 mesh size with 40% yield.

Detailed pilot scale tests were conducted on mixtures of different ore types in varying proportions. The results indicated that a grind of minus 20 mesh, with 10 percent of hard ore is essential for achieving the grade with 70 kWh/ton of concentrate energy requirement. The tests conducted in other laboratories in India viz., IBM etc., and overseas viz., Michigan Technological University, Ontario Research Laboratory, Nittetsu Mining Company, Dravo Corporation, Colorado School of Mines, IRISID of France, Grangesberg in Sweden, and Colerain Laboratory of US Steel confirmed the test results and generated additional parameters for designing purposes.

8. C O N C L U S I O N S

The role of pilot plant testing, its importance, advantages, disadvantages, essential and desirable data for pilot plant testing, unit operations, stages and the data obtained in a pilot plant testing, the pilot plant test report. Usages of pilot plant data in basic engineering and PTFR and conceptual design preparations have been also highlighted.

The pilot plant test is a key stage in project development process involving multidisciplinary team, large quantity of sample and producing valuable data and products where testing cost is less than 0.1% capital involved. It is advisable to do and involve in a continuous pilot plant testing to confirm the lab results and grain confidence in the process developed and market the products rather than having a frustrating posterior discussions on process failure as a commercial operation is not a R&D testing

ground. Turnkey testing programme both at lab, site from collection to plant stabilization.

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TABLE - 2

UTILITY OF PILOT PLANT DATA

SL.NO.

DATA PARTICULARS

UNIT PRODUCTS PURPOSE

1 Bulk density T/m3 Feed, Mill feed, Crusher

Sizing of bins, hoppers, volumetric flow rate for chutes, feeders etc.,

2 Density T/m3 All products For % solids & volumetric flow rate

3 Angle of repose o Feed, mill feed For sizing of stock piles etc. and dry tails

4 Shape sphericity % All products For selection of screen crushers etc.5 Hardness

AbrassivenessAll products For selection of construction

materials6 Size analysis Wt.% All products For equipment sizing7 Clay and

moisture content% Feed & tails For selection of crushers, scrubbers

& dewatering

8 Simulatory dataF/S, WI, UTA, FA

Feed, middlings, concentrates & tails

For flowsheet configuration and equipment sizing

9 Total chemistry %Feed, concentrate and tails

To ascertain valuable, harmful ingredients at every stage & its impact on economics & ecology

10 Specifications % Reagents, water & other supplies

For quality and purchase specifications

11 Mineralogical % & Size All products For diagnostic mineralogical amenability study

12 Test Work All products

a. Comminution Kwh/tFeed, mill feed, middlings

For operative energy requirements per tonne of ore and operative work index

b. Concentration All products

1. Metallurgical Balance

Wt.%, P. D, Assay % & Dist.%. Pulp volume, flow rate, size, water vol. and time

To ascertain metallurgy and material balance.

2. Water balance m3/hr/t,Water balance at every stage

To calculate water quality and quantity requirement at every stage

3. Energy balance Kwhr/t at every stage of unit operation

To calculate energy requirements at peak and normal level of operation

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TABLE – 2 (Cont.)

UTILITY OF PILOT PLANT DATA

SL.NO.

DATA PARTICULARS

UNIT PRODUCTS PURPOSE

4. Reagent Kg/t at desired points

For dosage, points of addition, dilution ratio and retention time

5. KineticsRate of conc. And commn. Products

Rate of concentration of values, size for efficiency determination w.r.t. time

6. Test work parameters

Grind size, PD, reagent dosage and time

To study the effect of parameters and develop regression equations

7. Process Stability

Statistical terms on flowsheet developed

Stability, sensitivity and guarantee of process and flow sheet developed

13Market specifications

Assay% size etcFor diverse usage, for having flexible flowsheets and trends of market for PTFR

14 Observations Process, products, equipments and flowsheet

Feasibility of flowsheet, engineering problems that may have to be encountered, marketing problems, operational and environmental hazards.

TABLE – 3

PILOT PLANT STUDIES INVOLVING MAGNETIC SEPARATION

Objective : To get magnetic concentrate/removal of iron impurities etc.

Equipment : type of separator viz. Low intensity, high intensity, electromagnet, permanent magnet (dry or wet)

Parameters:

Feed rate, % solids

Magnetic Intensity and matrix

Regrinding of middlings

RPM of the separator

Number of cleaning/ repasses

Air gap, belt speed, intensity, matrix in case of dry separator

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TABLE – 4

PILOT PLANT STUDIES ON IRON ORE FINES

Process : Wet scrubbing, Screening, Washing, classification, jigging/tabling

Objective: To develop a process flow sheet to produce a sinter feed + 63% Fe concentrate

Data:

Specific Gravity, Angle of repose, bulk density

Wet screening and jigging tests

Scrubbing, classification, tabling/ jigging tests

Parameters:

Scrubber feed rate, pulp density, trommel wash water rate, scrubber RPM,

Jig feed rate , stroke length, frequency,

Classifier slope, RPM, pulp density, launder water

Cyclone test parameters, thickening and dewatering tests

Material Balance flowchart and recommendations

TABLE – 5

COLUMN FLOTATION STUDIES

Amenability tests: to compare column flotation tests to agitation flotation cell

Process evolved in laboratory

MOG, % solids, reagents, flotation time to achieve results in conventional cells Operating conditions in column flotation

MOG, % solids, reagents, flotation time

Air flow rate and water flow rate to spargers, wash water flow rate, froth depth Varying residence time

Calculations

Superficial feed velocity

Superficial wash water velocity Superficial air velocity Residence time Sampling, grade recovery curve