FIELD OF THE INVENTION

The present invention relates to mineral transportation, and in particular to the

transportation of heavy minerals by pipe line.

BACKGROUND OF THE INVENTION

In the mining of minerals such as coal, zircon, rutile, gold, copper, zinc, bauxite, and

the like, the transportation of ore as well as the refined minerals often amounts to a

significant proportion of the overall production cost.

Conventional transportation systems include road links, rail networks, and ships.

However, these are relatively inefficient and place considerable demands on environmental

resources. Such forms of transport are also relatively inconvenient in that the product must

be moved batch wise, rather than continuously. In an attempt to address this problem, belt

conveyors have been used. However, these have generally been found to be unreliable,

impractical and financially non- viable over longer distances. They are also subject to

environmental influences, and cannot be used to transport minerals over water, for

example.

As a possible alternative to such conventional methods, numerous attempts have been made to transport minerals in slurry form along pipe lines. However, this has proven

to be problematic in practice. Particularly, in the case of dense ores, it has been found that

excessively high pumping pressures are required. This adds to the size, number and cost of

the pumps required, as well as to the cost of the pipe lines themselves which must be built

to withstand the higher internal pressures. Even then, only relatively low pumping speeds

can be achieved. It has also been found that conventional positive displacement type

pumps are unreliable and prone to rapid wear in such applications, typically because the

valve mechanisms cannot successfully accommodate large abrasive particles.

Furthermore, it has been found that dense phase slurries moving along pipelines are

particularly sensitive to vibration and pressure variations. Even relatively minor

disturbances of this nature can de-stabilise the moving slurry bed within the pipe line,

causing the dense particles to precipitate out of suspension from the carrier fluid, resulting

in blockages which are difficult to locate and clear. For these reasons, the transportation of

minerals by pipe line has, for the most part, proven to be commercially non-viable,

particularly over longer distances where the greatest economic potential for this mode of

transport resides.

It is an object of the present invention to provide an improved method which

overcomes or substantially ameliorates at least some of these disadvantages of the prior art.

DISCLOSURE OF THE INVENTION

Accordingly, in a first aspect, the invention as presently contemplated provides a

method of transportation of mineral ores, said method comprising the steps of crushing the

ore into relatively fine particles, mixing the crushed ore with a liquid carrier to form a

relatively high density mineral slurry, injecting a gas to aerate the slurry and produce a relatively low density mineralised froth, and pumping the aerated slurry and froth along a

fluid pipe line.

Preferably, the method includes the further step of adding a flocculating agent to the

slurry, thereby further reducing the density and stabilising the froth. Preferably also, a

soluble lubricant is added to reduce viscosity and facilitate pumping.

The method preferably comprises the further step of separating the desired minerals

from the froth at the remote end of the pipe line. The separation process preferably

includes one or more of: microwave heating; ultrasonic separation; cyclone separation; flotation; spraying; electrostatic precipitation; filtration; and drying.

In one preferred embodiment, a return pipe line flows upstream from the separation

station to a mixing station, whereby recovered flocculant, carrier liquid, and other additives

are recirculated and re-used.

In the preferred form of the invention, the pumping step is performed by a twin

cylinder positive displacement type pump with off-set pumping chambers and floating

unidirectional flap valves, thereby accommodating larger particles and producing a

relatively pulse-free output. Alternatively, however, a continuous flow peristaltic type

pump or other suitable pumps can also be used.

According to a second aspect, the invention provides an apparatus for transportation

of mineral ores, said apparatus comprising crushing means to crush the ore into relatively

fine particles, mixing means to mix the crushed ore with a liquid carrier to form a relatively

high density mineral slurry, injection means to inject a gas into the slurry thereby to aerate

the slurry and produce a relatively low density mineralised froth, and pumping means to

pump the aerated slurry and froth along a fluid pipe line.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is schematic view showing a long distance mineral transportation pipe line system including a pumping station according to the invention;

Figure 2 is an enlarged diagrammatic plan view showing the pumping station of

Figure 1;

Figure 3 is a diagrammatic cross-sectional view taken along line 3-3 of Figure 2,

showing the pump assemblies in more detail;

Figure 4 is an enlarged longitudinal section showing one of the floating flap valves

from the pumping station of Figure 2, with the valve in the closed position;

Figure 5 is an enlarged sectional plan view of the flap valve of Figure 4;

Figure 6 is a schematic view showing a typical hydraulic drive arrangement for the

pump assembly of Figure 3;

Figure 7 is an enlarged diagrammatic plan view showing an alternative arrangement

to the pumping station of Figure 2;

Figure 8 is a diagrammatic cross-sectional view taken along line 8-8 of Figure 7,

showing the pump assemblies in more detail; and

Figure 9 is a diagrammatic view showing the pumping station connected to a fluid

pipe line according to the invention, illustrating graphically the typical pressure and

velocity gradients.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring firstly to Figure 1, the ore is initially processed, crushed and reduced to relatively fine particles in a conventional processing plant 1. The crushed ore is then fed to

a belt conveyor 2 for transportation to a mixer 3. In the mixer, the crushed ore is mixed

with a liquid carrier, which may be mine water for example, to form a relatively high

density mineral slurry. The mixer includes programmable metering devices and feeders (not shown) for the crushed minerals, oxides or concentrates, the liquid carrier, flocculating

agents, plasticisers, lubricants and other components required to optimise the pumping

characteristics. The slurry is fed from the mixer 3 to a post-treatment station (not shown)

where gas is injected to aerate the slurry and produce a mineral enriched froth having a

relatively high degree of stability and relatively low density. The mineralised froth is then

fed to a pumping station 5, which will be described in more detail below. A nucleonic

flow monitoring device 5 A is positioned downstream of the pumping station to permit

constant monitoring and control over output velocity, flow rate and density. The froth then

flows into the main pipe line 6 for long distance transportation.

The pipe line terminates at a separation station 7 from which the ore 8 is recovered. The separation station 7 is shown diagrammatically as a cyclone separator. It will be

appreciated, however, that a number of separation processes such as cyclone separation,

flotation, spraying, electrostatic precipitation, filtration and drying may be used in order to

separate and concentrate the ore. The overflow from the separation station is directed to a

recirculation unit 9, and thence recirculated through line 10 back to the mixer 3 whereby

the recovered flocculant, carrier liquid, and other additives may be reused.

Upon aeration upstream of the pumping station, the dense slurry forms the walls of a

myriad of gas bubbles, which make up the mineralised froth. The size of the bubbles is

directly related to the dry density of the mineral ore and the density of the resultant slurry.

Ideally, the gas bubble and the surrounding slurry skin should result in a structure having

an overall specific gravity or relative density of less than 1.0. Due to the dramatic change

in density, the aerated slurry or froth has been found to be far more manageable in terms of

its pumping characteristics. In particular, it can be pumped at higher velocities with

considerably lower pressure requirements than would be required with untreated slurries.

In turn, this results in fewer and smaller capacity pumps, reduced pipe line diameter,

reduced pipe wall thickness, and in many cases enables the use of non-metallic pipes.

Figure 2 shows a first embodiment of a pumping station 5 in more detail. It will be seen that between the inlet 1 1 and outlet 12, the pipe line divides into two branches, 6A

and 6B. Each branch has an associated positive displacement pump cylinder 13 driven by

a double acting hydraulic actuator 14, and a pair of unidirectional floating flap valves 15

and 16. The cylinders and actuators 13 and 14 are shown in more detail in Figure 3, whilst the flap valves are shown in Figures 4 and 5.

Referring to Figures 2 to 5, it will be seen that as each pump cylinder 13 is displaced

downwardly by its actuator 14, the resultant pressure rise in the associated branch of the

pipe line causes the upstream flap valve 15 to close and the downstream valve 16 to open,

thereby forcing fluid through the outlet 12. The effect of this pumping phase is shown with

dark shading in branch line 6A. As each cylinder is subsequently withdrawn, the resultant

negative pressure in the associated branch line causes the downstream flap valve 16 to

close and the upstream valve 15 to open. The suction pressure then draws fresh fluid into

the branch line through the inlet 11. The effect of this suction phase is shown with dark

shading in branch line 6B. With the pump cylinders 13A and 13B operating 180° out of

phase, a substantially continuous flow is maintained. Moreover, because the flap valves

are free-floating, they are able to accommodate relatively large particulates without the risk

of mechanical failure and with minimal abrasive wear.

A typical hydraulic drive arrangement for the pump actuators 14 is shown in Figure

6, whereby a single control valve 18 is used alternately to direct driving fluid into the pressure chambers of each actuating cylinder. It will be appreciated, however, that

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alternative hydraulic, electrical or mechanical drive mechanisms may also be used, as may a variety of different pumps.

Figures 7 and 8 show a second embodiment of the pumping station 5 wherein,

corresponding features are denoted by corresponding reference numerals. In this case,

again, it will be seen that between the inlet and outlet, the pipe line divides into two

branches, 6 A and 6B. Each branch has an associated diaphragm type pump assembly 20,

as best seen in Figure 8. Each diaphragm pump includes a flexible diaphragm 21 movable

within a pumping chamber 22 by means of an hydraulic actuator or mechanical driver 23.

As with the previous embodiment, each pump acts in conjunction with a pair of

unidirectional floating flap valves 15 A, 15B, 16A and 16B, or other suitable alternatives

such as polyurethane ball valves, or gas or liquid operated pinch valves (not shown). The

hydraulic drive arrangement for the pump actuator, of the type shown in Figure 6, is also

suitable for use with the actuators 23 associated with the diaphragm type pump

arrangement shown in Figures 7 and 8.

Figure 9 shows a diagrammatic view of the pumping station 5 connected to a fluid

pipe line 6. Due to the stored energy contained in the compressed gas bubbles constituting

the froth, the media will travel in the pipe line form an initially compressed state at the

pump outlet, through a progressively decompressed state toward the pipe line outlet.

Consequently, the flow velocity at the inlet to the pipe line will be substantially less than

the delivery velocity at the outlet point. Typically, the velocity may vary from 0.05 metres

per second at the inlet to more than 3 metres per second at the discharge point of the pipe line. It will be appreciated, however, that the actual flow velocities will be dependent upon

a number of variables such as the volumetric flow rate and the pressure capacity of the

pump, the length and diameter of the pipe line, the nature of the materials being pumped,

the concentration of froth, and the like.

In Figure 9, the progressively increasing velocity gradient of the fluid is illustrated by

the graphical representation V _f , whereas the typical progressively reducing pressure profile

is represented graphically as P _f ' the parameter in each case being plotted against distance

along the pipe line. Again, however, it will be emphasised that the actual pressure and

velocity profiles will be subject to a number of variables and may not necessarily be linear.

It will also be noted that the rate at which material is drawn into each pump during

the suction stroke will be relatively constant, whereas the volume of fluid injected into the

pipe line during each compression stroke will vary, according to the pressure and load

status of the pipe line. Thus, as back pressure increases in the pipe line, a correspondingly

smaller volume of more highly compressed fluid will be injected during each compression

stroke. In this way, the pipe line acts a self-regulating damper, distributing pressure

relatively uniformly from the inlet end toward the open outlet. As the length of the pipe

line increases, its pressure characteristics resemble an open ended gas spring, with only

transient back pressure at the outlet of the pump.

The present invention enables dense mineral ores to be transported by pipe line over

relatively long distances at higher velocities, with lower pressures and with better reliability than have previously been achievable with dense phase slurries. This not only

increases transport range and throughput, but at the same time reduces the capital cost of

the pumps and pipe lines. The invention also allows a significant reduction in water

consumption, whilst power consumption is also significantly reduced. Further advantages

include a reduction in capitalisation cost, a reduction in operating cost, and substantially

reduced exposure of the ore to contamination by environmental and other influences. The

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invention thus considerably enhances the commercial viability of long distance mineral

transportation by pipe line, and thereby represents a significant improvement over the prior

art.

Although the invention has been described with reference to specific examples, it

will be appreciated by those skilled in the art that the invention may be embodied in many

other forms.