596 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Graphing some of the results found in Table 1, it is
possible to illustrate the impact of comminution on water
loss potential in two different ways. The first way is obvious
from the application of equation (14). Potential water loss is
proportional to comminution energy input (see Figure 2a).
Consequently, improving comminution grinding efficiency
affects directly the water loss potential of a given plant.
The second way is to examine potential water loss on a per
ton ore processed (see Figure 2b). In this case, the results
indicate that on a per ton processed basis, comminution
energy input is not necessarily the only indicator of water
loss potential. The difference between the two might point
to new opportunities to reduce water use.
AVENUES TO MITIGATE POTENTIAL
WATER LOSS
Having established that total water loss potential through
evaporation for the plant captured by a control volume is a
function of comminution energy input, the control volume
approach illustrated in Figure 1 can guide the investigation
of different avenues to reduce water loss of the 9 equipment
types found within a plant as illustrated in Figure 3.
1. The Plant
On a clear day at the equator, the solar energy (E
solar )
input averaged over 365 24 hour days is about 320 W/m2.
Assuming that most slurry carrying equipment in a plant
are exposed to the sun, the input energy is not negligible.
By adding an insulated roof, this input energy can be elimi-
nated from the plant. Furthermore, depending on how the
roof is designed and oriented, it can also serve as a means
to generate convection currents through the plant as well as
provide a platform for solar panels and electrical generation.
2. Tumbling Mills
All wet tumbling mills present two avenues for energy loss:
mass transfer due to evaporation and heat loss. In terms of
mass transfer (m
evap ),it is expected that this will be a func-
tion of the wetted surface inside the mill and the velocity
of air over that surface. The potential impact of this source
of water loss can be reduced by adding a shroud at the dis-
charge of the mill restricting and slowing air flow through
the mill. In terms of heat loss (Q
heat
o )through the cylindri-
cal wall, it is proportional to the thermal conductivity of
the liner and shell material used. Noting the difference in
thermal conductivities of steel and rubber (steel: 30 to 60
W/m-K rubber: about 0.1 W/m-K), it is expected that the
heat loss through the mill shell lined with steel liners will be
significantly greater than that with rubber liners.
3. Tall Stationary Equipment
This refers to equipment such as stirred mills, column cells,
and hydro-cyclones which have large non-moving shells.
Contrary to rotating equipment such as tumbling mills
where a convection current over the shell is inherent to
its operation, in stationary equipment this is not the case.
Consequently, potentially creating convection currents
over stationary equipment by an appropriately designed
roof could increase heat loss (Q
heat
o ).Heat loss over such
equipment can be increased further by adding fins to the
equipment. In this case, the choice of fin material such as
aluminium (Al thermal conductivity is about 100 W/m-K)
can enhance heat transfer through the shell.
4. Open Bodies of Water
This includes water reservoirs, thickeners, flotation cells,
column cells and sumps. However, before addressing
Figure 2. Potential water loss results
Graphing some of the results found in Table 1, it is
possible to illustrate the impact of comminution on water
loss potential in two different ways. The first way is obvious
from the application of equation (14). Potential water loss is
proportional to comminution energy input (see Figure 2a).
Consequently, improving comminution grinding efficiency
affects directly the water loss potential of a given plant.
The second way is to examine potential water loss on a per
ton ore processed (see Figure 2b). In this case, the results
indicate that on a per ton processed basis, comminution
energy input is not necessarily the only indicator of water
loss potential. The difference between the two might point
to new opportunities to reduce water use.
AVENUES TO MITIGATE POTENTIAL
WATER LOSS
Having established that total water loss potential through
evaporation for the plant captured by a control volume is a
function of comminution energy input, the control volume
approach illustrated in Figure 1 can guide the investigation
of different avenues to reduce water loss of the 9 equipment
types found within a plant as illustrated in Figure 3.
1. The Plant
On a clear day at the equator, the solar energy (E
solar )
input averaged over 365 24 hour days is about 320 W/m2.
Assuming that most slurry carrying equipment in a plant
are exposed to the sun, the input energy is not negligible.
By adding an insulated roof, this input energy can be elimi-
nated from the plant. Furthermore, depending on how the
roof is designed and oriented, it can also serve as a means
to generate convection currents through the plant as well as
provide a platform for solar panels and electrical generation.
2. Tumbling Mills
All wet tumbling mills present two avenues for energy loss:
mass transfer due to evaporation and heat loss. In terms of
mass transfer (m
evap ),it is expected that this will be a func-
tion of the wetted surface inside the mill and the velocity
of air over that surface. The potential impact of this source
of water loss can be reduced by adding a shroud at the dis-
charge of the mill restricting and slowing air flow through
the mill. In terms of heat loss (Q
heat
o )through the cylindri-
cal wall, it is proportional to the thermal conductivity of
the liner and shell material used. Noting the difference in
thermal conductivities of steel and rubber (steel: 30 to 60
W/m-K rubber: about 0.1 W/m-K), it is expected that the
heat loss through the mill shell lined with steel liners will be
significantly greater than that with rubber liners.
3. Tall Stationary Equipment
This refers to equipment such as stirred mills, column cells,
and hydro-cyclones which have large non-moving shells.
Contrary to rotating equipment such as tumbling mills
where a convection current over the shell is inherent to
its operation, in stationary equipment this is not the case.
Consequently, potentially creating convection currents
over stationary equipment by an appropriately designed
roof could increase heat loss (Q
heat
o ).Heat loss over such
equipment can be increased further by adding fins to the
equipment. In this case, the choice of fin material such as
aluminium (Al thermal conductivity is about 100 W/m-K)
can enhance heat transfer through the shell.
4. Open Bodies of Water
This includes water reservoirs, thickeners, flotation cells,
column cells and sumps. However, before addressing
Figure 2. Potential water loss results