Environmental Engineering Reference
In-Depth Information
Pintail Systems (Aurora, CO) has developed a biological process (USEPA, 1999) for the
removal of cyanide in a heap leach process. Native microorganisms were extracted from
the ore and tested for cyanide detoxiication potential. Those identiied were kept for
bioaugmentation purposes. Pilot tests were performed to simulate pile conditions and
determine detoxiication rates, process parameters, and efluent characteristics. Once the
test was complete, suficient quantities of bacteria were applied to the heap. Metals were
biomineralized during the leaching process. This process can be used for spent ore heaps,
waste rock dumps, mine tailings, and process water from silver and gold mining opera-
tions. The technology has been evaluated in the Demonstration Program and two full-
scale cyanide detoxiication projects were completed.
An anaerobic treatment process was developed by Geo-Microbial Technologies
(Ochelata, OK). The technology is called anaerobic metals release (AMR) instead of aero-
bic acidophilic bacteria that form acids and solubilize metal sulides. This acidiication can
contaminate streams and lakes. In contrast, the AMR technology uses
Thiobacillus
with a
denitrifying culture at neutral pH. The anaerobic conditions were controlled by the nitrate
levels in the leaching solutions, which allow solubilization of the metals. All nitrates were
consumed in the process. The metals are removed from the leachate by standard meth-
ods and the efluent is recycled. Levels of sulide-reducing bacteria and sulides are kept
to a minimum. The technology was demonstrated in a 1994 SITE Emerging Technology
Program.
5.2.3 Underground In Situ Hydrocarbon Extraction
The activities of interest in deep underground in situ hydrocarbon extraction include
(a) steam-based recovery of bitumen using the steam-assisted gravity drainage (SAGD)
process or a process known as the cyclic steam stimulated (CSS) process and (b) hydraulic
fracturing of deep underground shale and other geological formations containing natural
gas or tightly held oil for extraction of the hydrocarbon products.
The SAGD technique is a steam-assisted heavy recovery process where parallel wells
drilled into the deep underground are separated a few meters apart—with the top well
providing steam to the surroundings, and the bottom well serving as a collection well cap-
turing the gravity-assisted low of the luidized heavy oil as illustrated in Figure 5.4a. The
steam that is fed through the upper well to soften the heavy bitumen is delivered at pres-
sures below the fracture pressure of the host rock—thus allowing the luidized or softened
bitumen to low under gravitational forces into the collecting well below.
In the other technique, as the name implies, the CSS process uses a somewhat similar
procedure, i.e., introduction of steam into the geological formation of interest to soften the
contained bitumen. However, instead of utilizing gravity drainage of the softened bitu-
men into a parallel well below, the same well that provided the injected steam is used to
extract the softened bitumen—meaning that only a single vertical or horizontal well per
location is drilled. In short, the CSS technique uses the same well for both steam injection
and for extraction of the product bitumen. The cyclical procedure of steam injection fol-
lowed by extraction of the bitumen previously softened by the steam injection gives this
procedure its name CSS process.
Figure 5.4b shows the basic elements of the process commonly known as
fracking
, i.e.,
hydraulic fracturing of the host rock containing the hydrocarbons of interest (oil or natu-
ral gas). As with the CSS technique, a single horizontal well (per location) is drilled. A
common technique is to use a perforating gun inserted to the end of the well to initiate
small cracks in the penetrated host rock by detonating small charges. Subsequent crack
Search WWH ::
Custom Search