FINAL REPORT

to

MINNESOTA ENVIRONMENTAL QUALITY BOARDREGIONAL COPPER-NICKEL STUDY

Mineral Processing Studies

Dust Generation in Crushing and Handling

Mineral Resources Research CenterUniversity of Minnesota

Apri 1 24, 1980

This document is made available electronically by the Minnesota Legislative Reference Library as part of an ongoing digital archiving project. http://www.leg.state.mn.us/lrl/lrl.asp

FINAL REPORT

to

Minnesota Environmental Quality Board

Regional Copper-Nickel Study

Mineral Processing Studies

Dust Generation in Crushing and Handling

by

I. IwasakiK.A. SmithP.L. Glader

Mineral Resources Research Center56 East River Road

University of MinnesotaMinneapolis, Minnesota 55455

April 24, 1978

DUST GENERATION IN CRUSHING AND HANDLING

The purpose of the present investigation is to provide data that will

permit reasonable extrapolation on the amount and character of dusts to

be generated in the crushing and handling of copper-nickel bearing Duluth

gabbro. No direct measurements of dust concentrations near a pilot-plant

crusher operating on Duluth gabbro samples would simulate the real situation

in a crusher plant or the air effluent from the dust collection system. It

was proposed, therefore, that the following four sets of experimental data

be used to estimate by extrapolation the potential dust generated not only

in crushing, but also from conveyors, loading and transfer s~ons, and

storage piles.

1. "Dust data" in crusher building; and air effluents from

operating taconite plants.

2. Size distribution of crushed products from each stage

of the taconite plant crushing process, especially in the micron size

range.

3. Size distribution of the taconite samples crushed in each

stage of the MRRC pilot plant.

4. Size distribution of Duluth gabbro samples crushed in each

stage of the MRRC pilot plant.

Although such' an approach could not give precise quantitative information

the data could be utilized to estimate the dust generation potential in

a semi-quantitative manner.

Ideally, the "dust data" and the taconite samples should be collected

simul taneously. Several different taconite p'.ants with different degrees

of dust control facilities, including a plant meeting EPA new source

performance standards should be sampled. Furthermore, about half a

dozen samples of Duluth gabbro to cover a range of texture and degree

of mineralization should be included. The size distribution data of

both the taconite and Duluth gabbro samples in the MRRC pilot plant are

necessary since the distribution characteristics of crushed products

differ for different materials and for different crushers. Due to the

Copper-Nickel budget constraints, however, the number of taconite and

Duluth gabbro samples in the present report was limited to one s~Ple

each.

For comparative crushing studies of copper-nickel crude and taconite

samples approximately a one-ton sample of 4 to 6-inch lumps of copper-

nickel crude sample was hand picked from the AMAX Sample 2 pile. Three

drums of taconite lumps weighing in excess of one ton were received from

Erie Mining Company on November 22, 1977. The flowsheet for the crushing

studies, patterned after the Erie plant flowsheet, is shown below. The

crushers at MRRC were a lO-inch x 20-inch Traylor jaw crusher and a 2-foot

Symons cone crusher.

One-ton Sample

JJaw Crusher (-2 1/2 inch)

\

JCrushed Sample

Screen (1/8 inch)

1. d1.OverSlze Un erSlze

1Cone Crusher (-1 inch)

rCrushed Sample

The size distributions of the jaw crusher, minus 3/8-inch screen, and

the cone crusher products were determined using testing screens to 200 mesh

and then microscreens wet to 10 ~m. Originally, the minus 200-mesh fractions

were to be fractionated with an air classifier by the Donaldson Company, but

sufficiently large samples of the minus 200-mesh fractions were not obtained.

The results are given in Tables 1 and 2, and the size distribution data are

plotted in Figures 1 and 2 in terms of cumulative percent weight passing

versus particle diameter on a log-log paper. It is apparent both in the

tables and figures that the jaw crusher product of the taconite sample was

coarser than that of the Duluth gabbro sample, but that the size distributions

of the minus 3/8-inch screen products and the cone crusher products were

similar.

To investigate if the copper and nickel contents might segregate upon

crushing, the size fractions were combined in regular intervals and analyzed.

The analytical results are included in Table 2(a). Both the copper and nickel

contents showed tendencies to increase in finer size fractions. A head

sample was prepared by reconstituting the minus 3/8-inch screen product

and the cone crusher products in proportion to the weights and analyzed.

The head analysis is given in Table 3.

TABLE 3. HEAD ANALYSIS OF DULUTH GABBRO SAMPLE

Constituent Percent

Copper (Cu) 0.90

Nickel (Ni) 0.20

Cobalt (Co) 0.032

Iron (Fe) 12.99

Sulfur (S) 1.74

TABLE 1. SIZE DISTRIBUTIONS OF CRUSHED PRODUCTS OF ATACONITE SAMPLE FROM ERIE MINING COMPANY

-3/8" Cone CrusherJaw Screen Product Product

Crusher (5.07% (94.93%Size Product by Weight) by Weight)

+3 inch 41.12

+2 29.74

+1.5 9.91

+1 6.35 3.93

+0.742 3.38 16.85

+0.525 2.87 0.04 28.53

+0.371 1.93 0.07 18.69

+3 mesh 1.27 6.24 10.20

+4 0.79 14.44 5.33

+6 0.61 14.46 3.86

+8 0.46 12.24 2.82

+10 0.34 9.76 2.11

+14 0.25 7.90 1.36

+20 0.18 6.07 1.27

+28 0.14 5.01 0.93

+35 0.09 3.41 0.65

+48 0.09 3.64 0.70

+65 0.07 2.74 0.50

+100 0.06 2.38 0.42

+150 0.07 2.29 0.38

+200 0.05 1.59 0.19

+37 11m 0.10 3.37 0.47

+20 0.05 1.85 0.30

+10 0.03 0.83 0.17

-10 0.05 1.67 0.34

TABLE 2(a). SIZE DISTRIBUTIONS OF CRUSHED PRODUCTS OF MRRC LOT 2DULUTH GABBRO SAMPLE FROM AMAX

Jaw Crusher -3/8" Screen Product Cone Crusher ProductProduct (5.22% by Weight) (94.78% by Weight)

Size % Wt % Cu % Ni % Wt % Cu % Ni % Wt % Cu % Ni

+3 inch 35.78

+2 29.48 * *+1.5 8.47

+1 6.06 1.62

+0.742 3.29} 14.06 0.73 0.18+0.525 3.33 0.65 0.19 32.71

+0.371 2.36 o.lO} 18.82

+3 mesh lo67} 0.72 0.26 2.54 0.89 0.19 9.48} 0.80 0.18+4 1.16 7.28 5.10

+6 O.99} 0.86 0.25 9.00} 1.05 0.26 3.63} 0.90 0.20+8 0.79 8.20 2.62

+10 O.73} 1.03 0.255 7.S8} 1.07 0.27 2.0S} 0.96 0.225+14 0.62 6.78 1.54

+20 O.S8} 1.27 0.295 6.26} 1.17 0.28 lo28} 1.21 0.27+28 0.56 5.67 1.11

+35 O.4S} 1.20 0.26 S.64} 1.16 0.26 O.79} 1.28 0.275+48 0.53 5.62 1.01

+65 O.S6} 1.05 0.255 6.86} 1.16 0.265 O.86} 1.30 0.275+100 0.43 5.80 0.80

+150 o.71} 1.01 0.27 6.lS} 1.14 0.295 O.76} 1.40 0.31+200 0.37 3.97 0.53

-200 1.08 1.32 0.405 12.50 1.32 0.40 1.23 1.75 0.395

*Analyses not available

TABLE 2(b). SIZE DISTRIBUTIONS OF THE MINUS 200-MESH FRACTIONSOF CRUSHED PRODUCTS OF MRRC LOT 2 DULUTH GABBROSAMPLE FROM AMAX

Size

Jaw CrusherProduct

% Wt % Cu % Ni

-3/8" Screen Product(5.22% by Weight)

% Wt % Cu % Ni

Cone Crusher Product(94.78% by Weight)

% Wt % Cu % Ni

A. Sized by Microscreening

+37 llm 0.67 1.23 0.385 6.89 1.29 0.41 0.66 1.63 0.39

+20 0.16 1.45 0.50 2.18 1.40 0.45 0.21 1.55 0.40

+10 0.07 1.80 0.54 0.69 1.52 0.50 0.06 2.83 0.66

-10 0.18 2.16 0.39 2.74 2.17 0.31 0.30 2.29 0.38

Composite 1.08 1.45 0.41 12.50 1.52 0.40 1.23 1.84 0.40

B. Sized by Sedimentation Sizing

+37 llm 0.74 1.41 0.44

+20 0.16 1.07 0.32

+10 0.09 1.31 0.35

-10 0.09 1.29 0.30

Composite 1.08 1.34 0.40

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FIGURE 1. SIZE DISTRIBUTIONS OF CRUSHED PRODUCTS OF A TACONITE SAMPLE FROM ERIE MINING COMPANY

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FIGURE 2. SIZE DISTRIBUTIONS OF CRUSHED PRODUCTS OF MRRC LOT 2 DULUTH GABBRO SAMPLE FROM AMAX

In a separate investigation the minus 200-mesh fractions of pilot

plant flotation tailing samples were sized with microscreens and each

size fraction was analyzed for copper and nickel. The copper contents

of minus IO-~m fractions were noted to be unexpectedly high. Similar

trends were noted in the analytical results of microscreened fractions

of the presentsamples as shown in Table 2(b). Since all the water

samples used in microscreening (amounting to approximately 3 liters)

ended with minus IO-~m fractions and were removed by evaporation in

order to recover all the dissolved elements, the high copper contents

of minus IO-~m fractions were suspected to be due to dissolution

of the brass rims of the microscreens. Hence, the minus 200-mesh product

of the Jaw Crusher Product was fractionated into the same size ranges

using the sedimentation sizing method. The results shown in Table 2(b)

show that the copper content of the minus IO-~m fraction was appreciably

less and the composite analysis of the minus ZOO-mesh fraction was more

in line with the analytical data in Table 2(a). It is evident that the

sedimentation sizing method rather than microscreens should have been

used to avoid sample contamination.

The head sample and the minus lO-~m fractions of the three products

of the crushed Duluth gabbro were submitted to the Regional Copper-Nickel

Study for shipment to Barringer Research Ltd. for analysis of elemental

composition. The results received from Barringer are given in Table 4.

A comparison of the analytical results on the Jaw Crusher Product frac-

tionated by microscreening and sedimentation sizing, particularly those

of copper and zinc, suggests that the corrosion of microscreens affected

the analytical results of these two elements. Since the head sample and

the Jaw Crusher Product fractionated by sedimentation sizing were free

from such contamination, more importance should be given to these two

TABLE 4. TRACE ELEMENT ANALYSIS RESULTS IN PERCENT ON MRRCLOT 2 DULUTH GABBRO SAMPLE FROM AMAX AND ON MINUS10-~m FRACTIONS OF ITS CRUSHED PRODUCTS

Minus 10-~m Fraction of Crushed Products-3/8" Screen Cone Crusher

Jaw Crusher Product Product ProductHead (microscreen) (sedimentation) (microscreen) (microscreen)

Al 8.55 7.79 6.61 6.46 8.31

B

Be 0.00012 0.00009 0.00005 0.0001 0.00009

Ca 5.1 4.38 3.86 4.04 5.27

Cu 0.999 2.52 * 1.21 2.46* 2.63*

Fe 13.8 15.6 10.8 20.5 14.4

Mg 4.28 4.05 2.97 3.39 3.88

Mn 0.132 0.143 0.134 0.219 0.126

P nd nd nd nd nd

Ba 0.0258 0.0129 0.0667 0.0134 0.0098

Se

Te

As

Si

Sr 0.0239 0.022 0.0205 0.0189 0.0252

Zr 0.012 0.0116 0.00783 0.00884 0.0123

Ti 1.09 0.935 0.638 0.929 0.955

V 0.0162 0.0151 0.0096 0.0233 0.0135

Zn 0.0113 0.364 * 0.0579 0.41 * 0.257 *

Th 0.0004 0.0005 0.00049 0.0008 0.0007

K 0.767 0.655 0.596 0.61 0.593

Na 2.4 1.67 1.58 1.12 1.92

Cd nd nd 0.0009 nd nd

Cr 0.0126 0.0132 0.0141 0.0017 0.014

Co 0.018 0.0263 0.0191 0.0239 0.0258

Ag 0.0002 0.0007 0.0008 0.0007 0.0008

Mo 0.0008 nd 0.002 0.0027 nd

Ni 0.17 0.346 0.21 0.284 0.326

Pb 0.005 0.024 0.012 0.0265 0.029

*Contamination through corrosion of microscreens suspected

sets of data. It is evident that copper, zinc, silver and nickel tended

to increase their concentrations somewhat in the 'dust' fraction upon

crushing, indicating that sulfide minerals were broken to finer sizes

more readily, but all the other elements did not change their concentrations

significantly.

SUMMARY

Duluth gabbro and taconite lumps crushed through a pilot plant jaw

crusher and cone crusher gave similar size distributions. Therefore,

it was surmised that the dust generation potential in crushing Duluth

gabbro would be similar to that in the existing crushing facilities

for taconite. Though sulfide minerals tend to break somewhat preferen­

tially, there were no unusual concentrations of any trace elements in

the potential dust fraction.