1989-11-22_REVISION - M1988112

• Permit No: M1988112
• IBM Index Class Name: Revision
• Doc Date: 11/22/1989
• Doc Name: TAILINGS COLUMN TESTING PROCEDURES BATTLE MTNS SAN LUIS PROJECT
• Type & Sequence: AM1
• Media Type: D
• Archive: No

~. In the absence of calcareous material,
the pH of the ground water could be leas
than 5.5 due to the carbonic acid reaction.
In this case the natural ground water system
can support the catalyzing iron bacteria
and if an acid problem exists, their pre-
sence serves to compound the problem. How-
ever, if calcareous material is present,
the pll of the ground water regime tends to
be in the alkaline range, which inhibits
the iron bacteria and reduces the acid
potential.
The pH of [he water is also important
in stabilizing certain types of pyrite.
Temple and Koehlerb showed that calcium and
magnesium (presumably as a Calcium-magnesium
carbonate) were present in stable pyrite
modules, but absent in the reactive ones.
Significantly, washing the nodules with a
mild hydrochloric acid caused the inert
samples to become reactive. This suggests
that once acidic waters are formed, the
pyrites are effectively leached of their
protective carbonates and perpetuate the
acid producing reactions.
Factor Interactions and Predictions of Mine
Drainage Quality
The principal factors affecting mine
drainage quality have been identified as:
(i) Alkalinity - a function, in part,
of the amount of calcareous mate-
rial present in the strata;
(ii) pH - controls the occurrence of
the catalyzing iron bacteria and
affects the preservation or dis-
solution of pyrite stabilizing
carbonate; and
(iii) the nature and distribution of
acid-producing pyrite.
These three factors have been organ-
ized into a conceptual model that is shown
in Figure 1. In the hydro-geochemical
c I - '~ ~I - ~ri4 Y Yw
E II - ~a `.r
ll I~~
y I , ^ - r.......
E
r• -
_ ~\ r
9 III ~ Y -....
nnn~bu.~on of Pn~.e B.aew XwluLa na
c.,... s~., rov.la yen oo.~,l, .l
c,...d w.l..
Fiy ure 1. Conceptual model relating mine
dra,nage quality to various hydro-geochemi-
cal factors.
environment I, the pyrite is primarily
coarse grained and relatively slow reacting,
the calcareous material present renders the
pH of the ground water above 6.4 (which
inhibits the catalyzing iron bacteria) and
generates highly alkaline, strongly buffered
aqueous regimes. In this envirorunent, the
minor amounts of acidity produced by the
coarse pyrite are neutralized by the alka-
linity, the acid reaction is not catalyzed
and the pyrite stabilizing carbonates, if
present, are preserved. In hydro--geochemical
environment I, the mine drainages are chem-
ically neutral and have low sulfate con-
centrations. '
At the other end of the spectrum, in
hydro-geochemical environment III, most of
the pyrite is fine grained and rapidly oxi-
dizes to produce abundant acidity. In the
absence of calcareous material, the pH of
the ground water is low and thus supports
the iron bacteria that can catalyze the
acid reaction. The lack of calcareous mate-
rial also produces low alkaline-lightly
buffered ground waters (low specific con-
ductance) that are easily degraded by the
acidity produced. Mine drainages in this
environment have high acidity, sulfate and
specific conductance.
Hydro-geochemical environment. II repre-
sents the average of the two, wittl cor-
respondingly moderate amounts of acidity and
sulfate.
Neutral-high sulfate drainages are
created when strongly alkaline graund waters
come in contact with acid mine drainages.
Such a geologic system may represent strata
having the potential to produce highly
acidic, high sulfate drainage, but which are
capped by glacial material that has the po-
tential to produce highly alkaline waters.
In this environment, the acid waters are
neutralized by the alkaline raters to pro-
duce neutral high sulfate type mine drainages.
On a larger geographic scale the con-
ceptual model can be related to the paleo-
environment (the depositional environment)
of the strata which enhances the model's
predictive capability. In this case, the
marine-brackish water pa leoenvironment is
readily identified with hydro-geochemical
environment III, whereas the fresh water
pa lecenvironmen is are closely rel acted with
hydro-geochemical environment I. 9y mapping
the paleoe nvizonment of an area, the poten-
tial of mines located in a particular
stratum to produce acid can be discerned in
a general way.
The Assessment of a Stratum's Capability to
Produce Acidic Drainage
Mine Drainage Characterization. As shown
in the first part of this paper the quality
of mine drainage that emanates from a strip
mine is determined by a va rie[y of factors,
including: ground eater geochemistry, mode
of pyrite distribution, hydrology ~~f the
mine site, occurrence of calcareous mate-
rial, the presence of iron bacteria and [hc
manner in which all of these are allowed [o
479