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The
Circulating Load
Practical Mineral Processing Plant
Design by an Old-Time Ore Dresser
Robert S. Shoemaker
Published by the
Society for Mining, Metallurgy, and Exploration, Inc.
© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
Society for Mining, Metallurgy, and Exploration, Inc. (SME)
8307 Shaffer Parkway
Littleton, Colorado, USA 80127
(303) 948-4200 / (800) 763-3132
www.smenet.org
SME advances the worldwide mining and minerals community
through information exchange and professional development.
Copyright© 2002 Society for Mining, Metallurgy, and Exploration, Inc.
Electronic edition published 2009.
All Rights Reserved. Printed in the United States of America
No part of this publication may be reproduced, stored in a
retrieval system, or transmitted in any form or by any means,
electronic, mechanical, photocopying, recording, or otherwise,
without the prior written permission of the publisher.
Disclaimer
Any statement or views presented here are those of the author
and are not necessarily those of the Society for Mining,
Metallurgy, and Exploration, Inc. The mention of trade names for
commercial products does not imply the approval or endorsement
of SME.
ISBN 978-087335-308-3
© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
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C
ONTENTS
Preface v
1 Primary Crushers 1
2 How to Clean Up a Dirty Dump Pocket 3
3 Sampling a Ball Mill 5
4 Vibrating Feeders 7
5 Notes on Conveyors 9
6 Storage Bins 16
7 The Design and Operation of Floors 20
(From the Mill Operator’s Standpoint)
8 Determining Velocities in Pipelines the 26
Easy Way
9 Notes on Fines 27
10 Overengineering 32
11 Cage Mills, Impactors, and Hammer 35
Mills
12 Environment Controls for Grinding Mills 38
13 That Odious Pump 40
14 Never Hire a Plumber Who Claims to 43
Be a Pipefitter
15 Pilot Plants 45
16 Precious Metals Column and Heap 49
Leaching Pilot Plants
17 Sumps, Pumps, Etc. 51
18 Foolproof Plug Valves 55
19 Design for Maintenance 57
20 Mexican Feeders 61
21 Supervising the Engineer–Constructor 63
© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
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© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
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P
REFACE
In 1964 when I became chief metallurgist of
Bechtel’s Mining and Metals Division in San
Francisco, I was fortunate to be able to see not
only the minerals processing plants that
Bechtel was designing and building but many
others designed and built by other engineering
firms. When I was in an area that had such
plants other than the one I was visiting, I
found that the managers and mill
superintendents of these plants were most
hospitable in showing me their operations and
freely answered any questions I asked. During
those visits I observed many clever ideas in
plant design developed by the plant operators
and other engineering firms and also many
mistakes that resulted in higher capital and
operating costs. The mistakes, by the way,
were not limited to other engineering firms as
we were not by any means omniscient and
bloodied our noses as often as did others.
As a result of these observations and in
order to improve our engineering capabilities,
I started writing down what I (and some of my
metallurgists) had seen and distributing the
ideas not only to my people but also to the
chief engineers in our other disciplines. These
publications were called The Circulating Load
and, very often, clients who had seen them
would ask for back copies and to be put on the
mailing list. These people would often copy
them and send to their friends in the industry.
v
© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
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THE CIRCULATING LOAD
On the cover sheet of each issue were the
words “Published frequently in the interest of
fewer spills in the mill.”
In this rewrite I have recaptured the best
incidents from the past and added some
observations and recollections from the last
twenty years as a consultant. It is hoped that
these practical methods will be of help to all
the mill men who have made the mineral
processing industry what it is today.
vi
© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
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THE CIRCULATING LOAD
1
PRIMARY CRUSHERS
We got one of our best ideas concerning
primary crushers from a 54- × 74-inch
gyratory crusher installed at the Ray Mines
division of Kennecott Copper. This crusher had
a rubber belt feeder under its surge pocket—
one that we believe to be the first ever
installed. It was 6 feet wide and about 80 feet
long and was also used as a picking belt to
remove timbers that came from the old
underground mine. The total height of the
installation from the belt feeder floor to the top
of the dump pocket was 63 feet. The belt,
which also handled old drill steel and
miscellaneous scrap iron, had a life of about
14 months and handled 10 million tons in
that time.
When we were designing the Similkameen
copper plant in British Columbia for Newmont,
Frank McQuiston and I spent many hours
discussing the possibility of using an 8-foot-
wide belt under the 54- × 74-inch gyratory
crusher we planned to install there. There were
several advantages that finally tipped the
scales to the belt feeder rather than an apron
feeder. The belt feeder was 40 feet long so that
it permitted the downward-sloping takeaway
conveyor to be straight instead of having a
reverse vertical curve. The belt feeder required
less height than an apron feeder, did not
require the height for a takeaway conveyor
under an apron feeder, and lastly, because of
its width, permitted more live storage and less
1
© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
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THE CIRCULATING LOAD
height in the surge pocket under the crusher.
The capital cost savings was very substantial,
and the total height from the feeder floor to the
edge of the dump pocket was only 59 feet.
When we last heard, the belt feeder had
handled 120 million tons of the hard, jagged
Similkameen ore without an hour of
unscheduled downtime. The few gouges it had
sustained were repaired with liquid rubber
during regularly scheduled downtime.
Newmont had purchased a spare belt, and
Rolly Nice, the plant manager, told us that if
the belt should ever need replacing they could
probably never unroll the spare belt as it was
so old. A few months after this crusher was
completed, Gibraltar also installed an 8-foot
belt feeder under their new crusher, and we
used a belt feeder under the third gyratory at
Palabora. Many other belt feeders have been
used by others since then. Unfortunately, a few
apron feeders are still being installed under
primary crushers.
This (the Similkameen) was the first gyratory
crusher we ever installed without using an
overhead crane. Newmont had purchased an
80-ton mobile crane to lift the bodies on their
100-ton trucks, and this crane was capable of
handling the 45-ton crusher mantle. After a
year’s operation we talked to Similkameen’s
manager and mill superintendent and asked
their opinions on the crusher installation. They
told us that when they arrived on the site
before operations had begun they had been
very apprehensive about maintaining the
crusher, and visitors from other British
2
© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
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THE CIRCULATING LOAD
Columbia copper plants had predicted doom
and destruction when they had seen this
“cheap” installation.
Actual operation had, however, proved all
their prognostications wrong. The first relining
job using the mobile crane had taken 48
hours—no record of course, but very
creditable, considering it was the first crusher
relining job for the maintenance crew. They
were certain the second relining could be done
much faster. (A similar first relining job we
know of using an overhead traveling crane at
another plant required 87 hours.) To say the
least, the manager and superintendent were
very pleased.
2
HOW TO CLEAN UP A DIRTY
DUMP POCKET
Dust collection or suppression at primary
crusher dump pockets has always been such a
problem that many people have simply ignored
it with the idea that dump pockets have always
been dusty and always will be. (At the time of
this re-editing, in 2002, the rules have been
radically changed and such dusty conditions
are rarely tolerated. However, the ideas
presented here are the best we have ever seen
and could be of use at a number of mines I
have seen recently.) The problem here is the
enormous, but momentary, need for dust
collection volume during and shortly after a
3
© 2002 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.
