Mine Water I – Formation and Treatment
Example questions
Write the four most important aspects of the following image.
A.: The image aims to highlight the fact that an understanding on
mine water and its reactions with ore deposits/ waste dumps, the
protection of water bodies (underground and surface ones), and
the protection (access cleansed water) of all the stakeholders are
important.
The image reflects the fact that mining activities are everywhere
in the world. Humans and economies rely on mining for almost
every activity or service: energy provisions, construction materials
or to fabricate items. As such, mining cannot be avoided. Furthermore, in some cases, as a
product of mining activities, mine water is generated and hence it needs to be remediated to
minimize the environmental impact.
Write the four most important aspects of the following image.
A.: The image aims to highlight the fact that to develop
remediation and control measures of acid mine drainage,
the following aspects of the surrounding environment
need to be comprehended: geological, geochemical,
hydrogeological, mineralogical and biological ones. The
factors that occur in a waste dump and can enhance the
acid mine drainage (water runoff, oxygen advection,
seepage, infiltration, saturated and undersaturated flow,
and evaporation/thermal convection) are described in the
image. Furthermore, the most important components for
acid mine drainage to occur are sulfide minerals, oxygen, water and bacteria. Lasty, once sulfide
minerals are oxidized, sulfate and heavy metals are dissolved and mobilized through tailings and
the underlying aquifers.
Write the four most important aspects of the following image.
A.: The image shows a portable photometer test kit that enables
the determination of some ions concentration such as Fe (II), Fe
(III) or sulfate. This type of analysis is important to investigate
whether there is acid mine drainage generation in case it is at an
early stage. Noteworthy is the fact that if the acid mine drainage
(amd) process is not at the initial phase, a visual inspection of the
water (reddish color or the existence of iron precipitates) is
enough to determine that amd is occurring. Lastly, a photometer
is required to quantify the amd process.
Write the four most important aspects of the following image.
A.: The image reflects a guideline criterion for choosing mine
water treatment methods based on the flow rate and
contamination concentration. As such, if both the flow rate and
the contaminant concentrations are low, monitoring and natural
attenuation are sufficient. In the case where the flow rate and
the contaminant concentrations have medium values, passive
mine water treatment methods are recommended. Lastly, if the
flow rate and the contaminant concentrations are high, active
treatment methods may be required.
Write the four most important aspects of the following image.
A.: A striping column is a columnar device with filling material (glass
beads) which aims to create an interaction between the liquid and
gas flows which are in counter-current (being this process known
as aeration). Hence, the dissolved gases (mostly CO2) are degassed
and consequently released from the water. It is noteworthy that
the filling material aims to create a large contact area between the
water and the air, turning the separation process more efficient.
Furthermore, in this process, Fe (II) and other dissolved species can
oxidize due to the presence of oxygen.
Write the four most important aspects of the following image.
A.: The image shows a sketch diagram from a Wismut modified lime
precipitation plant to treat mine water. The key aspects of this
process are the initial addition of HCl to convert carbonate and
bicarbonate into CO2 which is then removed in the stripping column.
In this step, the dissolved elements are oxidized too. BaCl2, FeCl3 and
Ca(OH)2 are added to precipitate sulfate (and coprecipitate the
available radium), to increase the iron concentration to a minimum
level that triggers Fe(OH)3 precipitation, and to increase the pH promoting the precipitation of
several contaminants, respectively. Moreover, flocculants such as alumina are added to the
water to facilitate the settlement and consequent removal of the formed precipitates. Lastly,
cement is added to immobilize the dry residue of filter pressing which is disposed afterwards.
Write the four most important aspects of the following image.
A.: During remediation, mine water is separated from waste that
can be hazardous. In this case, the originated sludge was
considered as hazardous waste. As such, to dispose it, the
established regulations needed to be respected and precautions
should exist. Hence, above and below the big bags that contained
the waste, geomembranes (to prevent water infiltration that can contaminate the aquifers),
drainage layers to collect circulating water inside the system, antifreeze layers and cement were
emplaced.
Write the four most important aspects of the following
image.
A.: The image illustrates a former lignite mine in the
Zwenkau region where the pyrite oxidation promoted the
existence of acid mine drainage. Due to the fact that there
was a deficient drainage rainfall water, an acidic lake was
formed. Later on, the lake was flooded and a
neutralization plant was built to remediate the water
during several years. When totally remediated, the lake provided recreational services.
Write the four most important aspects of the following image.
A.: The image shows ion exchange columns being used in an
American underground mine. Initially, the inflow water had a low
pH (around 4) and both the copper and cobalt concentrations had
high values (30 and 0,3 mg/L, respectively). After treated in the
plant, the outflow had a neutral pH and the copper concentration
decreased significantly (0,01 mg/L), as well as the cobalt
concentration (0,002 mg/L). It can be stated that the ion exchange
technique can be used in both open pit and underground mines to treat waters resulting from
the acid mine drainage process.
Write the four most important aspects of the following image.
A.: The image illustrates the ion exchange process in a real-case scenario, where
the boy is a functional group and two girls are ions with the same charge. First,
there is a couple at a given class that is not tightly bonded. Later on, a charming
new girl joins the class and the boy falls in love with her. As such these start to have
a relationship because the boy picked the second girl over the first and this last has
to end her initial relationship.
Write the four most important aspects of the following image.
A.: The image reflects the composition of a resin (polymer ion
exchanger). On the polymer backbone, there are copolymerized
functional groups where the bond is firm, being impossible to
separate these two components. The functional groups have a charge
(either positive or negative): if the charge is negative, the resin is a cation exchanger and if the
charge is positive, the resin is an anion exchanger. In order to neutralize/ balance the charge, an
opposite charge is introduced/adsorbed and this process can be preferential depending on the
ion’s affinity towards the functional group.
Write the four most important aspects of the following image.
A.: The ion exchange process cycle is composed by four steps: service or loading,
backwash, regeneration and rinse or conditioning. The first aims to pump mine water
into the exchange column, where the present contaminating ions are adsorbed by the
resin and the previously retained ions are desorbed. The backwash process consists on
adding distilled water, promoting the removal of the present mine water and nonadsorbed ions. Next, during regeneration the resin saturated with contaminating ions
is cleaned by removing and recovering these ions with acid that promotes the desorption of the
ions and the adsorption of H+. Lastly, the rinse process consists on restoring the system to its
initial state, where the original ions are provided (being adsorbed) by pumping a sodium or
calcium-based hydroxide solution into the column.
Write the four most important aspects of the following image.
A.: The image corresponds to a breakthrough graph which is
used to interpret the loading or regeneration results. The
abscissa axis corresponds to the effluent/ bed volume or the
time, whereas the ordinate axis provides the ion concentration
within the effluent. At the beginning of the loading cycle the
effluent has a negligible concentration and, at a given point,
the contaminant starts to be present in the effluent (the
breakthrough point is reached), once the column is walking
towards exhaustion and therefore, its concentration rises. In this graph, Co corresponds to the
initial ion concentration in the mine water and when the column is exhausted (the exhaustion
point is reached) the effluent’s ion concentration is equal to Co.
Write the four most important aspects of the following image.
A.: The image shows a patented ion exchange mine water treatment
plant used in a South African gold mine. After being neutralized, the
water was pre-treated to remove uranium and it was further directed
to the ion exchange plant. First, two cation exchange columns in
series remove the cations and then two anion exchange columns in
series remove the anions, being the residues sold to the explosives
and chemical industries. It should also be noted that nitric acid and
coal were used in the regeneration process of the cation exchange columns and ammonia was
used in the anion columns.
Write the four most important aspects of the following image.
A.: The image represents a reverse osmosis pressure vessel. To realize
this process at an industrial scale, a spiral wound reverse osmosis
element is used inside a pressure vessel, where a feeding solution
circulates through it and a feed water carrier (scaler/ mesh) creates
turbulence, increasing the internal pressure. Moreover, the feed water
carrier creates a channel where the water flows. After passing through
a series of semi-permeable membranes, the permeate (purified solution) is collected with the
help of a permeate carrier material which delivers the solution to a perforated product tube,
whereas the concentrate/retentate enriched in undesired elements is collected in a separate
volume.
Write the four most important aspects of the following image.
A.: The image shows an ion exchange mine water treatment plant
that was tested in Russia with a flow of 24 m3/day. The main aspects
of this plan are the existence of two ion exchange columns that were
used to adsorb copper and nickel and these were monthly
regenerated with sulfuric acid. After this step, the water was softened
with sodium carbonate (the hardness was removed by insolubilizing
calcium). Then, after a series of steps, the water was disinfected
during two different stages before being considered as cleansed.
Write the four most important aspects of the
following image.
A.: The image shows a batch reactor and
reverse osmosis mine water treatment plant
that was tested in South Africa. The key aspects of this example are the addition of magnesite
to increase the pH, facilitating the precipitation of metals such as Fe, Al, and Mn as hydroxides;
the addition of lime is important to precipitate magnesium and sulfate as brucite and gypsum,
respectively, reducing the water hardness; and soda ash was used to recover residual calcium
(as limestone) and magnesium, reducing the water hardness.
Write the four most important aspects of the following image.
A.: The image represents a grain-size curve for tailings (percent
passing vs. grain diameter) produced after a milling stage in Canada.
It can be noted that the tailings vary over a wide range of grain sizes.
As such, each tailings pile within an impoundment is
stratigraphically unique. Furthermore, for sandy and silty particles
(such as tailings) there is a proportional relationship between the
hydraulic conductivity and the effective particle size (D10).
Write the four most important aspects of the following image.
A.: The image shows a suction lysimeter that can be used in the tensionsaturated zone to sample pore-water. The main reason for sampling the
vadose zone within tailings impoundments is to control sulfide oxidation
and other acid mine drainage-related processes that can occur in this zone.
It is noteworthy that due to the fine grain texture of tailings, the water
content in the unsaturated zone of impoundments can be high.
Furthermore, once in silty sediments the capillary fringe may extend
several meters above the water table, a constant monitoring using devices
like lysimeters is required.
Write the four most important aspects of the following
image.
A.: The image illustrates an engineered structure of natural
wetlands: an aerobic constructed wetland, being the
reactions in this the same as in a natural system. These structures contain an impermeable layer
or liner that prevents seepage and further soil/ aquifer contamination. The hydraulic retention
time, the water level and the soil emplaced in these wetlands provide the necessary support for
the vegetation’s roots. Moreover, when the iron content is higher, more aeration steps are
required to oxidize the iron, being this enhanced by cascades or riffles.
Write the four most important aspects of the following image.
A.: The image shows an anoxic limestone drain that is
normally used for net acidic mine waters that have low
dissolved oxygen, Fe (III) and Al (III), once these metals can
precipitate, clogging the pores. Nevertheless, clogging is
limited to the first 10 or 15% of the limestone bed. These systems are always flooded to keep
anoxic conditions. It should also be noted that anoxic limestone drains tend to be buried to
increase the CO2 partial pressure, producing high alkalinity concentrations.
Write the four most important aspects of the following image.
A.: The image shows a constructed wetland system
implemented at the Pöhla mine, in Germany. This system of six
ponds was efficiently used to treat mine water at a low cost,
having the outflow a contaminant concentration below the
discharge limit. The most important aspects of this system are
the settlement pond where iron and arsenic coprecipitate and
the pond with Characeae algae that accumulate high quantities of radium.