A Laboratory-Scale Magnetohydrostatic 

Separator and its Application to 

Mineralogic Problems 

By HENRY V. ALMINAS, TERRIL. MARCEAU, JAMES D. HOFFMAN, 

and ROBERT C. BIGELOW 

U.S. GEOLOGICAL SURVEY BULLETIN 1541 

Construction plans, operational 

instructions, and some data on 

the instrument's effectiveness 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1984 
UNITED STATES DEPARTMENT OF THE INTERIOR 

WILLIAM P. CLARK, Secretary 

GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Library of Congress Cataloging in Publication Data 

Main entry under title: 

A Laboratory-scale magnetohydrostatic separator and its application to mineralogic problems. 

(Geological Survey Bulletin ; 1541) 

Includes bibliographic references. 

Supt. of Docs. No.: I 19.3 

1. Magnetic separation of ores. 2. Calutron. 

I. Alminas, Henry V., 1938- II. Series. 

QE75.B9 no. 1541 557.3s [622'. 77] 83-600204 [TN530] 

For sale by the Branch of Distribution 

U.S. Geological Survey 

604 South Pickett Street 

Alexandria, VA 22304 
CONTENTS 

Page 

Abstract 

Introduction . 

MHS principle 

1 

1 

2 

MHS separator construction 3 

MHS separator operation . . 11 

14 

20 

21 

Results obtained with MHS separator 

Summary .... 

References cited 

FIGURE 1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

ILLUSTRATIONS 

Diagram showing the relative height of suspension of grains of 

quartz, fluorite, barite, and galena in a paramagnetic solution 

Page 

within a magnetic field . . . . . . . . . . . . . . . . . . . . . 3 

Photograph of a magnetohydrostatic (MHS) separator 5 

Plans for a specialized MHS mounting table and a modified Frantz 

Isodynamic Separator base plate . . . . . . . . . . . 6 

Plans of modified pole pieces used for MHS separator . . . . . 7 

Plans of separation chamber . . . . . . . . . . . . . . . . . . . . 8 

Diagram showing proper separation chamber orientation relative to 

the electromagnet pole pieces . . . . . . . . . . . . . . 9 

Schematic diagram of the MHS separator . . . . . . . . . . . . 10 

Plans of custom-made components for the MHS separator . . . 12 

Graph showing solution flow rate versus precision of separation in 

the MHS separator . . . . . . . . . . . . . . . . . . . . . . . 14 

Diagram showing the behavior of mineral grains of varying specific 

gravity and magnetic susceptibility within the separation 

chamber while separator is in operation . . . . . . . . . . . 15 

Graph showing amperage settings on the MHS separator versus 

specific gravities of suspended minerals . . . . . . . . . . . . 16 

Graph showing specific gravity ranges of 11 nonmagnetic minerals 

versus amperage values required for 100 percent suspension. 17 

Graph showing specific gravity ranges of six partially magnetic minerals versus amperage values required for 100 percent suspension . . . . . . . . . . . . . . . . 17 

Suspension curves for 18 selected minerals . . . . . . . . . . . . 18 

TABLE 

Page 

TABLE 1. Water-soluble paramagnetic salts and their magnetic susceptibilities 4 

III 

A LABORATORY-SCALE 

MAGNETOHYDROSTATIC SEPARATOR 

AND ITS APPLICATION TO 

MINERALOGIC PROBLEMS 

By HENRY V. ALMINAS, TERRI L. MARCEAU, 

jAMES D. HOFFMAN, and ROBERT C. BIGELOW 

ABSTRACT 

Tests of a newly designed laboratory-scale magnetohydrostatic separator (MHS) indicate an alternative to the standard heavy-liquid separation techniques currently in use 

in the U.S. Geological Survey. 

An MHS separator is based on the principle that a paramagnetic solution placed 

in an inhomogeneous magnetic field will exhibit an apparent specific gravity directly 

proportional to the magnetic field strength. An aqueous solution of MnCl2·4H20 at 

a concentration of 150 g/100 mL, placed in the magnetic field, becomes an instantly 

variable heavy liquid, ranging in density from 1.4 to >9.0. Nonmagnetic minerals are 

affected only on the basis of their specific gravity characteristics. Partially magnetic 

minerals are affected through a combination of their specific gravity and magnetic susceptibility characteristics and react as if the specific gravities of these minerals were 

higher than, in fact, they are. Magnetic minerals are pulled out of the solution by 

the magnet. 

INTRODUCTION 

This study was initiated in 1978 to determine whether methods 

other than the standard heavy-liquid techniques could be used to make 

mineral separations on the basis of specific gravity. The experimental 

area of MHS (magnetohydrostatic) separation techniques was chosen 

as showing the most promise at that time. 

The authors designed, constructed, and operated an MHS separator 

that uses an aqueous paramagnetic solution (manganous chloride) to 

test the behavior of some common minerals, the rate and cleanliness 

of mineral separation, and the applicability of the separator to routine 

U.S. Geological Survey operations. Studies are currently underway 

to determine the applicability of ferro-fluids (a water-base suspension 

of miniature magnetite crystals) to this device. 

The term magnetohydrostatic (MHS) was coined by U. Andres, who 

did much of the original experimental work in the definition of the 

principles of this phenomenon, as well as its applicability to industrial 

processes. 
2 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

MHS PRINCIPLE 

A magnetohydrostatic separator is based on the principle that when 

a paramagnetic solution (or ferro-fluid) is placed within an inhomogeneous magnetic field, it will exhibit an apparent specific gravity directly proportional to the magnetic field strength. Thus, in a 

container filled with a paramagnetic solution placed within a wedgeshaped air gap between the pole pieces of an electromagnet (fig. 1), 

the apparent specific gravity of the solution will be highest in the 

zone of maximum constriction and will decrease progressively upward, 

as illustrated by the suspension levels of galena, barite, fluorite, and 

quartz (fig. 1). These nonmagnetic mineral grains were displaced to 

those portions of the magnetic field where the solution has an equivalent apparent specific gravity. Partially magnetic minerals will show 

an increase in apparent specific gravity, similar to the increase in 

the paramagnetic solution, and will be accordingly suspended lower 

than their true specific gravity would dictate. Magnetic minerals 

(those having a magnetic susceptibility equal to or greater than that 

of the solution) will simply collect at the strongest portion of the magnetic field. Andres (1976) notes that, for most purposes, the following 

equation can be used for the calculation of MHS separation: 

where 

fo 

J.11 

J.12 

H 

body force; 

magnetic permeability of the liquid medium; 

magnetic permeability of the mineral particle; 

magnetic field strength. 

(1) 

Solutions of any number of soluble paramagnetic salts (table 1) could 

be used in an MHS separator. For practical purposes, the overriding 

considerations in the choice should be nontoxicity, magnetic permeability, low corrosiveness, stability, and cost. These considerations make 

manganous chloride one of the better choices. 

The magnetic susceptibility of a salt is dependent on the amount 

of magnetophoretic ions in it. The magnetic susceptibility of a 

paramagnetic solution depends on the solubility of the paramagnetic 

salt in water, in addition to the salt's magnetic susceptibility. The 

bulk magnetic susceptibility of an aqueous paramagnetic salt solution 

can be calculated by the following equation: 

(2) 
MHS SEPARATOR CONSTRUCTION 

i 

PARAMAGNETIC SOLUTION 

N s 

POLE PIECES 

0 Quartz 

[g] Fluorite 

§ Barite 

• Galena 

FIGURE 1.-Relative height of suspension of grains of quartz, fluorite, barite, and galena in a paramagnetic solution within a magnetic field. 

where 

X 

xi 

c 

(0. 724 . 10-6) = 

bulk susceptibility of solution; 

magnetic susceptibility of salt; 

concentration of salt in water; 

magnetic susceptibility of water. 

3 

Measurements by U. Andres, using the Gouy method, indicate that 

the highest magnetic susceptibilities at room temperature are exhibited by solutions of MnC12 and Mn(N03) 2• The higher specific gravity 

and viscosity of the Mn(N03) 2 solution make it less desirable than 

the MnC12 solution. 

MHS SEPARATOR CONSTRUCTION 

The MHS separator described in this report (fig. 2) was constructed 

around a modified Frantz Isodynamic Separator1

, which is used to 

provide the required magnetic field. The modifications are such that 

1

Use of brand or manufacturers' names in this report is for descriptive purposes only and does not constitute 

endorsement by the U.S. Geological Survey. 
4 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

TABLE I.-Water soluble pammagnetic salts and their magnetic susceptibilities · [From Andres (1976] 

Molar Molar Volume 

Salt sugcept i bili ty weight sugceptibility 

(10 CGSM units) (10 CGSM units) 

CoBr 2-------- 13,000 219 59 

CoC12--------- 12,600 130 98 

Dy2(S04)3---- 45,700x2 539 170 

Er 2(so4 ) 3 "8H2o 37, 300x2 768 97.5 

EuBr 2--------- 26,800 312 85.7 

EuC12--------- 26,500 223 118.5 

Eui2---------- 26,000 406 64.0 

Euso4--------- 25,730 248 104.0 

FeC12-------- 14,750 136.8 108.0 

FeC13--------- 13,450 172 .o 78.5 

Feso4-------- 10,200 152.0 67.5 

GdC13--------- 27,930 263.0 106.0 

Gd2(so4 )3---- 27, 160x2 602.0 90.0 

MnBr 2--------- 13,000 215.0 61.0 

MnC1 2--------- 14,350 126.0 114.0 

MnF2---------- 10,700 74.0 145.0 

Mni 2---------- 14,400 309.0 46.6 

MnS04--------- 13,660 151.0 91.0 

NiBr 2--------- 5,600 218 25.7 

NiC12--------- 6,145 130 47.4 

Tb2(so4) 3----- 39,160x2 706 111.0 

the Frantz can be easily reconverted to its original purpose and consist 

of: 

1. The cutting of a rectangular hole in the Frantz base plate, as 

shown in figure 3, and 

2. The replacement of the standard Frantz pole pieces with the 

modified ones shown in figure 4. 

Plans for a specialized table for mounting the MHS separator are 

also shown in figure 3. 

With the new pole pieces in place, the electromagnet is oriented 

with the pole-piece air gap upward and the long axes of the pole 

pieces running front to rear. The magnet is tilted forward so that 

the plane formed by the tops of the pole pieces makes a 45° angle 
MHS SEPARATOR CONSTRUCTION 

FIGURE 2.-The U.S. Geological Survey's magnetohydrostatic 

(MHS) separator. 

5 
6 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

142.2 

91.4 

5.1 

A 

SIDE VIEW 

117 

30.5 

5.1 

("-. 

L- 58.4 -----J 

FRANTZ BASE 

39.4 

~~527l 1.9 y: r:::=J } 6 0 

l l16.J y 

7.6 FRONT 

3s 

} 6 .4 

126 

}5.1 

55.9 

J 

}5.1 

~ 

5.1 

A 

n 

~ 

26 

117 

~ 

FRONT VIEW 

5.1 

A 

I 

l 61.0 _J 

TABLE TOP 

}6.4 

} 5.1 

} 5.1 

rfs~610~l 

20.3 t ...... j_ 1.3-cm 

2 5 t::-- diameter . ,- ,- 58.4 

r-22.91 J j__~ c=J } 7.6 

10.2 !----------J 

Tl---+--10.2 

FRONT 

FIGURE 3.-Plans for a specialized MHS mounting table and a modified Frantz 

Isodynamic Separator base plate. All measurements in centimeters. 
T 

r--

C") 

l 

MHS SEPARATOR CONSTRUCTION 

Taps for Y. inch x 20 bolt, 

1.2 inches (3.1 em) deep 

( b k d f I 

/on ac Sl eo poe p1ece'\ 

25.4 / \ 

\ 

r/ ··1-· - - - ---- -------------- _1----------~ - --------\~ .j __ I 

-/ '/ 

/PROTRUDING EDGE 

7 

J 

_I 

r L 7.7* 5.0~ 

FRONT VIEW OF LEFT POLE PIECE 

*Note : These measurements will be reversed on right pole piece 

I~38~~9~ 

l 3 8 ~ ~ l '-------J 

END VIEW 

Outline of allen-head bolt 

used on Frantz separator 

FIGURE 4.-Plans of modified pole pieces used for MHS separator. Measurements in 

centimeters except as noted. The new pole pieces should be machined from the mildest available steel to minimize residual magnetism. 

with the horizontal. A Plexiglas separation chamber (fig. 5) is mounted 

within the air gap as shown in figure 6. It is important that the wedgeshaped splitter within the separation chamber be in line with or somewhat above the line formed by the narrowest portion of the air gap. 

Within the paramagnetic solution, light mineral grains float above the 

level of this line and exit the chamber through the upper tube, and 

the heavier grains fall below this level and are removed through the 

lower tube. It is also important that the separation chamber be 

positioned in such a manner that mineral grains entering it via the 

inlet tube fall vertically into progressively stronger portions of the 

magnetic field rather than being trapped in the back portion of the 

chamber behind the magnetic field. 

Figure 7 is a schematic diagram of the MHS separator with the 

electromagnet omitted. The heavy arrows indicate that portion of the 

separator through which the sample flows. The various components 

of this portion must be connected with glass tubing and ball and socket 
8 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

SIDE VIEW 

Socket joint-, 

(0.0 . =1 .2 ; 1.0 . = 0.5) 

Spacer 

Spacer 

~-!:'f:=.:;Q:::.T--Rectangular 

(X) 

brass tubing 

0 .34 X 0.62 

j lt----+---Round brass tubing 

Ground glass ball joints 

(1.0. =0.5; 0.0. =1.2) 

(0 .0 . =0.47) encased 

by glass tubing 

(1 .0. =0.48) 

L.() 

tWall Plexiglas 

thickness =0.1 5 

TOP 

VIEW 

Spacer Plexiglas . 

thickness =0.3 

FIGURE 5.-Plans of separation chamber for the MHS separator. All measurements 

in centimeters. 
MHS SEPARATOR CONSTRUCTION 

FIGURE 6.-Proper separation chamber orientation relative to the electromagnet pole pieces. 

9 
10 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

SYSTEM -FILLING 

PRESSURE BULB 

SAMPLE FEED-RATE 

NEEDLE VALVE 

THREE -WAY 

COUPLER 

EXPLANATION 

-==:::J Direction of sample flow 

Direction of fluid flow 

+ Stopcock 

+ Ball and socket joint 

CATCHMENT 

SEPARATORY 

FUNNELS 

RECOVERY FUNNELS 

ELECTRONIC 

LIQUID-lEVEL 

CONTROLLER 

TOP STORAGE 

TANK 

NONMAGNETIC 

~LIGHT M INERALS 

~ OVERFLOW 

LINES 

SYSTEM AIR -BLEED 

VALVE 

FLOW EQUALIZATION 

CHAMBER 

SOLUTION 

FLOW-RATE 

FLOW METER 

ON~AY VALVE 

FIGURE 7.-Schematic diagram of the MHS separator. 
MHS SEPARATOR OPERATION 11 

joints to permit easy passage of particulate matter. The balls and 

sockets are lightly coated with silicone stopcock grease to prevent 

leakage. The fine arrows indicate the portion of the system through 

which solution flow occurs. The components within that portion of 

the system where only solution flow occurs can be interconnected with 

flexible plastic tubing. 

In addition to the pole pieces and separation chamber, the sample 

catchment funnels, the flow equalization chamber, the three-way 

coupler, and the sample feed funnels were custom made, and plans 

are shown in figure 8. The other components are commercially available items and are listed below: 

Two (top and bottom) tanks (rectangular plastic 15-L containers) 

Two needle valves (200 mL/min range) 

One liquid-flow meter (100 mL/min range) 

Two plastic funnels 

One 250-mL gas-washing bottle used as filter 

One one-way ball valve 

One %sth-horsepower electric pump 

One electronic liquid-level controller 

MHS SEPARATOR OPERATION 

Before a sample is introduced into the separator, certain steps are 

advisable: 

1. If a sample is rich in clays, it should be washed to remove 

most of them. Clays will flocculate in the solution and clog the 

system. 

2. The sample should be sieved to ensure that the largest mineral 

grains are smaller than the smallest opening within the mineralflow path. 

3. Strongly magnetic minerals (such as magnetite, ilmenite, and 

maghemite) should be removed from the sample to prevent excessive buildup within the separation chamber. 

This MHS separator can be operated with or without solution flow. 

The same equipment and orientation are used in both instances. Solution flow speeds up the separation process but somewhat reduces separation precision. The decrease in precision is the result of the complexity of motion occurring within the separation chamber; that is, 

the movement of the grain relative to the fluid and of the fluid relative 

to the chamber walls. As flow rate is increased, grain configuration 

and grain size become important factors in determining whether the 

grain goes into the light or heavy fraction. Turbulent flow occurs within the separation chamber as a result of high flow rates and tends 
12 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

T 

0 

'<t 

OPENINGS =0.4 ~ 

GROUND GLASS 

BALL JOINT 

0 .0 . =1.2 

1.0. =0.5 

SAMPLE FEED 

FUNNEL 

SOCKET 

1.0. =0.5 

THREE-WAY 

COUPLER 

(X) 

ui 

/SOCKET 

0.0. =1.2 

1.0. =0.5 

0 .0 . =0.8 

1.0 . =0.5 

0 .0. = 0 .65 

1.0.=0.4 "==~=-< 

CATCHMENT 

SEPARATORY 

FUNNEL 

N 

-0.0. = 0 .8 

1.0. = 0.5 

FLOW 

EQUALIZATION 

CHAMBER 

FIGURE 8.-Plans of custom-made components for the MHS separator. All measurements in centimeters. 
MHS SEPARATOR OPERATION 13 

to force light minerals into areas of higher solution specific gravity. 

Figure 9 shows the behavior of the light fraction under various rates 

of solution flow. 

The graphs shown in the "Results" section were established using 

a system flowing at the rate of 30 mL/min. In this mode, there is 

continuous solution flow through the system while the separator is 

in operation. Starting at the top storage tank (fig. 7), the solution 

flows through the sample feed-rate needle valve, the three-way 

coupler, the separation chamber, the two catchment separatory funnel 

overflow lines, the flow equalization chamber, solution flow-rate control valve, flow meter, and into the bottom storage tank. Here the 

solution accumulates until it reaches a preset level, at which point 

the electronie liquid level controller activates a pump to force the 

solution through a filter (adapted gas-washing bottle) and a one-way 

valve back into the top storage tank. The desired solution flow rate 

is established by opening the top tank stopcock and the sample feedrate needle valve and then adjusting the solution flow-rate valve to 

the proper setting. The desired magnetic field strength is established 

by adjusting the variable rheostat controlling the electromagnet current (read in amperes). 

The sample is introduced into the partly filled sample feed funnel 

and is thoroughly wetted with solution using a wash bottle. The funnel 

is capped with a soft rubber stopper equipped with an overflow line 

leading into the top storage tank. Sample flow is established by opening the stopcock at the bottom of the sample feed funnel and simultaneously adjusting the sample feed-rate needle valve until the desired 

rate of sample flow is established. The back pressure of the solution 

flowing up into the sample feed funnel permits one to establish and 

maintain a uniform sample flow rate over a wide range. Upon leaving 

the sample feed funnel (fig. 7), the sample material drops vertically 

through the three-way coupler into the vertical portion of the separation chamber. Here, the sample material, somewhat spread out by 

the solution flow, sinks till the various mineral components reach the 

level at which the solution has an equivalent apparent specific gravity. 

The nonmagnetic light-mineral fraction (fig. 10) slides along in a series 

of closely spaced stratified layers above and parallel to the line of 

the maximum air-gap constriction, passes above the splitter, and exits 

through the pper line into a catchment separatory funnel. The partially magnetic and nonmagnetic (at this amperage) heavy-mineral 

fraction drops to the bottom of the separation chamber and is saltated 

via the lower exhaust tube into a catchment separatory funnel. The 

grains of the magnetic fraction become attached to the chamber walls 

along the maximum air-gap constriction and are retained within the 

chamber until the electromagnet is turned off. 
14 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

(f) 

-;iz 

ffig 

Zf-

-u 

~<( 

>- a: 40 >u.. 

<(fUJI 

I<.9 

u..::J 

Oo 

f-fzz 

w-

~ @20 wu a_<( 

f-_l 

I a_ 

(.9~ 

ijjQ 

s: 

SOLUTION FLOW IN MILLILITERS PER MINUTE 

FIGURE 9.-Solution flow rate versus precision of separation in the MRS separator. 

The light- and heavy-mineral fractions can now be drained into the 

filter paper-lined funnels, and then the magnetic fraction can be recovered by turning off the electromagnet and catching the material in 

the heavy-fraction catchment separatory funnel. The sample material 

in the filter funnels can be washed with water and dried on a hotplate. 

The separator can be cleaned between samples by opening the fluid 

flow control needle valve wide open for some time and removing any 

mineral grains that might get flushed down into the catchment 

separatory funnels. A more vigorous flushing can be obtained by opening both catchment separatory funnel stopcocks. Cleanliness can be 

completely ensured by draining and refilling that portion of the system 

between the sample feed funnel and the tops of the catchment separatory funnels. 

If the separator is operated without solution flow, the sample is 

introduced into the open sample funnel via a vibrator-mounted hopper 

attached to the rod above the funnel. The sample feed rate is governed 

by a variable rheostat controlling the vibrator. The sample flow pathway and sample recovery are the same as described for the solution 

flow mode. 

RESULTS OBTAINED WITH MHS SEPARATOR 

The graphs shown in this section were established using the following sample preparation and separator parameters: 

1. The mineral samples were crushed and sieved to > 107 and <503 

J.Lm (165to 38 mesh). 
RESULTS OBTAINED WITH MHS SEPARATOR 

e FELDSPAR 

• QUARTZ 

.PYRITE 

A MAGNETITE 

FIGURE 10.-Behavior of mineral grains of varying specific gravity and 

magnetic susceptibility within the separation chamber while separator 

is in operation. 

15 
16 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

....J 

<X: 

a: 

8.0 

~ 7.0 

~ 

0 

w 

0 

z 

g: 6 .0 (/) 

::. 

(/) 

u_ 

0 

i:: 5.0 

> <X: 

a: 

(.9 

u 

u::: u 4.0 

w 

c... 

(/) 

3.0 

2.0 

0.7 0 .9 1.1 1.3 1.5 1.7 1.9 

CURRENT TO MAGNET, IN AMPERES 

FIGURE H.-Amperage settings on the USGS magnetohydrostatic separator versus 

specific gravities of nonmagnetic minerals suspended in the MnC12 solution. Caution: 

identical amperage settings on other MHS separators will probably produce different specific gravities. Each device should be calibrated separately. 

2. The sieved sample material was washed with water to eliminate 

the dust coating that collected on the grains during the crushing. 

3. A 5-gram sample was used to establish each point on the graphs. 

4. The separator was operated in flowing solution mode with a 

flow of 30 mL/min. 

5. The solution concentration used was 150 g MnC12 ·4H20/100 mL 

H20, which produced a specific gravity of 1.42 at 24°C. 

The graphs are plotted to show weight percent of mineral suspended 

at a given amperage. In using this information, it is important to 
6.0 

>-

I-

> 

~ 

a: 

c.? 5.0 u 

u:: 

u 

lU 

c.. 

CJl 

4.0 

3.0 

2.0 

0.5 

RESULTS OBTAINED WITH MHS SEPARATOR 

4 

I 

23 

i' 

1 

0 .7 

9 

I 

8 

7 I 

6 

I 

5 

0 .9 1.1 

10 

I 

1.3 

1 . 

2 . 

3 . 

4 . 

5 . 

6 . 

7 . 

8. 

9. 

10. 

11 . 

1 1 

I 

1.5 

CURRENT TO MAGNET, IN AMPERES 

MICROCLINE 

QUARTZ 

ALBITE 

APATITE 

FLUORITE 

SPHALERITE (light) 

BARITE 

ZIRCON 

CHALCOCITE 

ARSENOPYRITE 

GALENA 

1.7 

17 

1.9 

FIGURE 12.-Specific gravity ranges of 11 nonmagnetic minerals versus amperage 

values required for 100 percent suspension. 

6.0 I I I I I I I I I I I I I 

1. DIOPSIDE f2 . PYRITE -

>- 3. CHALCOPYRITE 2 I-

> 5.0 I- 4 . SPHALERITE (dark) I -

~ 

a: 5. OLIVINE c.? 6 . MALACHITE 5 - u 3 

u: 14 6 

u 4 .0 - I - lU 

c.. 

CJl 1 

I -

3 .0. I I I I I I I 

0 .5 0 .7 0 .9 1. 1 1.3 1.5 1.7 1.9 

CURRENT TO MAGNET, IN AMPERES 

FIGURE 13.-Specific gravity ranges of six partially magnetic minerals versus amperage values required for 100 percent suspension. 

keep in mind that the actual magnetic field strength produced by any 

two Frantz electromagnets, at a given amperage reading, will differ 

somewhat. This variance may be brought about by a number of factors, such as ammeter error, slight differences in coil winding, or 
100 

90 

80 

0 

w 70 0 

z 

w 

c.. 

(/) 

::J 60 

(/) 

Iz 

w 50 u 

a: 

w 

c.. 40 II 

~ 

w 30 ~ 

20 

10 

0 0

.50 

0.60 0.70 

0.80 

0.90 1.00 1.10 1.20 1.30 

CURRENT TO MAGNET, IN AMPERES 

1.40 

1--' 

00 

> 

t'-4 

> to 

0 

~ 

> 

~ 

0 

~ 

~ 

w. 

n 

> t'-4 

tr:l 

a.:: 

> C1 

z 

tr:l 

~ 

0 

:I: 

~ 

t::J 

~ 

0 

U'1 

;; 

~ -

n 

U'1 

tr:l 

"'0 

> 

~ 

~ 0 

~ 
100 

/ 

..,...o .,. o· o' / / o--v o "" / 1/ (/ LLENA // "" 

801- / 

.,. .-o 

I v i I _.;"" 

@ 70 I 0 / / 0 I I / 

z I I 0 

UJ 0 I I 

f}j 60 I I I ::> I 0 I (/) I 

f-oLIVINE 

I 

1- PYRITE I 1

t-- MALACHITE 

rE 50 0 

I I I u I a: I I I UJ I c... 40 I I I I 1-

I I I I (.9 I 0 I 

UJ 30 CHALCOPYRITE I I 

3;: I 

I 

ARSENOPYRITE-! 

20 

10 

1.30 1.40 1.50 1.60 1.70 1.80 

CURRENT TO MAGNET, IN AMPERES 

FIGURE 14.- Suspension curves for 18 selected minerals, showing percentage of each mineral suspended in the MnClz 

solution versus amperage flowing to the electromagnet on the MHS separator. 

~ 

tr:1 

rn 

d 

t"' 

--3 

rn 

0 

Oj 

--3 

> z 

trl 

t:1 

~ 

~ 

i:I: 

~ 

i:I: 

rn 

rn 

trl 

~ 

> 

~ 

> --3 

0 

~ 

~ """"" 
20 A LABORATORY-SCALE MAGNETOHYDROSTATIC SEPARATOR 

slight differences in the air-gap dimension or pole-piece construction. 

As a result, the actual field strength produced at various amperage 

readings should be checked for each instrument used. 

The field strength of the electromagnet used to establish these 

graphs was checked at 10 places along the long axis of the pole pieces 

and has a range of 10,460-10,600 gauss and an average of 10,564 gauss 

at 1.0 ampere. 

The configurations of the low- and high-amperage ends of the individual mineral curves (fig. 14) to a degree reflect the impossibility 

of obtaining pure mineral samples. Some of the curvature also results 

from intramineral fractionation brought about by variation in specific 

gravity due to metamictization, hydration, crystal imperfections, substitutions in the crystal lattice, and inclusions of other minerals or 

by the variation in magnetic susceptibility due to staining, substitution 

in the crystal lattice, and inclusion of other mineral species. 

Figure 11 is a plot of specific gravity against amperage. The line 

gives empirically determined amperages at which a nonmagnetic mineral of a given specific gravity can be suspended. Figure 12 shows 

the specific gravity ranges and amperages required for 100 percent 

suspension for 11 nonmagnetic minerals. Figure 13 shows the same 

for six weakly magnetic minerals. Figure 14 shows individual mineral 

suspension curves for 18 selected minerals. 

For geochemically oriented routine application, this separator will 

process approximately 1 g/min of pan concentrate at a-bromoformequivalent setting and a solution flow rate of 30 mL/min. At this processing rate, approximately 1 percent of the heavy-mineral fraction 

will consist of light minerals. 

SUMMARY 

For most purposes an MHS separator can be used as an alternative 

to the traditional heavy-liquid techniques to separate minerals on the 

basis of specific gravity. Of equal or greater interest is the potential 

of this instrument in solving specialized mineralogic problems requiring high-specific-gravity separation, fine specific gravity differentiation in the range of 1.4 through >9, or single-pass separation capability based on specific gravity and magnetic susceptibility simultaneously. Listed below are some of the advantages offered by this method 

of separation: 

1. The device uses an essentially nonvolatile, nontoxic, and totally 

nonflammable solution (Friberg and others, 1979). 

2. No special installations, such as hoods, are required. 

3. Subsequent to installation, operating costs are extremely low. 
REFERENCES CITED 21 

4. The method makes available the equivalent of an instantaneously variable heavy liquid that has a specific gravity range 

of 1. 4 through 10 for all nonmagnetic minerals and a more restricted range for weakly magnetic minerals. 

5. It has a single-pass separation capability, based on specific gravity and magnetic susceptibility simultaneously. 

Some of the disadvantages inherent in the system are as follows: 

1. Initial setup is relatively expensive. 

2. The sample handling capability of the device is limited by the 

strength of the available electromagnet. 

3. The device is unable to separate the more magnetic minerals 

on the basis of specific gravity. 

4. The paramagnetic solution has greater corrosiveness than the 

most common heavy liquids. 

5. The operator training period is longer than that required for 

standard heavy -liquid techniques. 

REFERENCES CITED 

Andres, U., 1976, Magnetohydrodynamic and magnetohydrostatic methods of mineral 

separation: New York, John Wiley and Sons, 224 p. 

Friberg, Lars, Nordberg, G. F., and Bouk, Velimir, eds., 1979, Handbook on the 

toxicology of metals: New York, Elsevier/North Holland Biomedical Press, 

709p.