|
Reduction in ARD parameters after 19 weeks by combined
<br />phosphate and thiocyanate treatment of sulfidic waste rock in
<br />laboratory humidity cell tests. P rock + SCN = phosphate rock
<br />plus thiocyanate treatment, Dical + SCN = agricultural (more
<br />soluble) phosphate plus thiocyanate treatment.
<br />and phosphate treatment dramatically
<br />reduced ARD production (see chart
<br />above) by controlling both chemical
<br />and biological oxidation of sulfides.
<br />Thiocyanate improves the stability and
<br />longevity of iron phosphate coatings and
<br />precipitates because it stops microbially
<br />catalyzed reactions that generate extremely
<br />acidic conditions.
<br />Field performance, however, is the
<br />key criterion of success. Researchers
<br />began tests in summer 2004 at the Red
<br />Dog zinc -lead mine in northwestern
<br />Alaska to evaluate whether thiocyanate
<br />and phosphate can control oxidation of
<br />sulfides in waste rock. The waste rock
<br />contains zinc sulfide and pyrite as the
<br />primary sulfide minerals. Waste rock
<br />in 600 -ton lined test pits was dosed
<br />with combinations of thiocyanate and
<br />phosphate. It was then leached with
<br />rainfall and snowmelt only. Results from
<br />the first season showed that following
<br />initial washout of soluble salts, leaching
<br />of ARD parameters using the combined
<br />treatment was reduced 50 to 70 percent
<br />compared to untreated rock. The test will
<br />continue next year.
<br />The cost of the combined treatment is
<br />about $1 per ton of waste rock but can
<br />be further reduced if phosphate rock is
<br />found to be effective and practical at large
<br />scales. This cost is much lower than other
<br />proposed source control technologies. Key
<br />questions being addressed in field trials
<br />are longevity of the treatment, the most
<br />effective forms and dosages
<br />of thiocyanate and phosphate,
<br />and the best methods of
<br />application.
<br />Although thiocyanate and
<br />phosphate are relatively
<br />benign, releasing them
<br />into receiving waters in
<br />elevated concentrations is
<br />undesirable. The preferred
<br />approach to ARD control is
<br />to minimize the use of these
<br />chemicals, thereby avoiding
<br />their presence in seepage or
<br />drainage. Drainage or seepage containing
<br />these chemicals can be recycled or treated
<br />using active or passive processes in a
<br />relatively inexpensive and straightforward
<br />manner.
<br />Source control of ARD using chemical
<br />treatments is a promising approach, but
<br />must be incorporated in a comprehensive
<br />plan that includes applying the
<br />treatment during placement of was
<br />te
<br />rock and minimizing infiltration of
<br />precipitation. Consequently, the semi -arid
<br />Southwest may be a good location for
<br />this technology.
<br />HydroFacts
<br />Average annual flow of the Colorado River: 15 million acre -feet
<br />Storage capacity of Colorado River reserv
<br />oir system: 60 million acre -feet
<br />Water in storage as of December 2004: about 35 million acre -feet
<br />Low reservoir level impact on hydropower production, Hoover Dam, 2003 -1993: -15%
<br />Low reservoir level impact on hydro
<br />power production, Glen Canyon Dam, 2003 -1993: -30%
<br />Cost to build Hoover Dam Visitors' Center, 1992 -1995: over $100 million
<br />Cost to build Hoover Dam, 1930-1935:
<br />$49 million
<br />Cost to build Hoover Dam in 1933, adjusted for inflation to 1993 -4 dollars: $550 million
<br />Total Dissolved Solids, Colorado River headwaters: 70 mg /liter
<br />Total Dissolved Solids, Colorado River at U.S.-Mexico
<br />border: 800 mg /liter
<br />March /April 2005 •Southwest Hydrology • 11
<br />■ DicaI +SCN
<br />Y 30
<br />❑ Control
<br />25
<br />�-
<br />E P rock +SCN
<br />20
<br />L
<br />d 15
<br />9 10
<br />E
<br />� 5
<br />° sulfate acidity iron arsenic (x100)
<br />Reduction in ARD parameters after 19 weeks by combined
<br />phosphate and thiocyanate treatment of sulfidic waste rock in
<br />laboratory humidity cell tests. P rock + SCN = phosphate rock
<br />plus thiocyanate treatment, Dical + SCN = agricultural (more
<br />soluble) phosphate plus thiocyanate treatment.
<br />and phosphate treatment dramatically
<br />reduced ARD production (see chart
<br />above) by controlling both chemical
<br />and biological oxidation of sulfides.
<br />Thiocyanate improves the stability and
<br />longevity of iron phosphate coatings and
<br />precipitates because it stops microbially
<br />catalyzed reactions that generate extremely
<br />acidic conditions.
<br />Field performance, however, is the
<br />key criterion of success. Researchers
<br />began tests in summer 2004 at the Red
<br />Dog zinc -lead mine in northwestern
<br />Alaska to evaluate whether thiocyanate
<br />and phosphate can control oxidation of
<br />sulfides in waste rock. The waste rock
<br />contains zinc sulfide and pyrite as the
<br />primary sulfide minerals. Waste rock
<br />in 600 -ton lined test pits was dosed
<br />with combinations of thiocyanate and
<br />phosphate. It was then leached with
<br />rainfall and snowmelt only. Results from
<br />the first season showed that following
<br />initial washout of soluble salts, leaching
<br />of ARD parameters using the combined
<br />treatment was reduced 50 to 70 percent
<br />compared to untreated rock. The test will
<br />continue next year.
<br />The cost of the combined treatment is
<br />about $1 per ton of waste rock but can
<br />be further reduced if phosphate rock is
<br />found to be effective and practical at large
<br />scales. This cost is much lower than other
<br />proposed source control technologies. Key
<br />questions being addressed in field trials
<br />are longevity of the treatment, the most
<br />effective forms and dosages
<br />of thiocyanate and phosphate,
<br />and the best methods of
<br />application.
<br />Although thiocyanate and
<br />phosphate are relatively
<br />benign, releasing them
<br />into receiving waters in
<br />elevated concentrations is
<br />undesirable. The preferred
<br />approach to ARD control is
<br />to minimize the use of these
<br />chemicals, thereby avoiding
<br />their presence in seepage or
<br />drainage. Drainage or seepage containing
<br />these chemicals can be recycled or treated
<br />using active or passive processes in a
<br />relatively inexpensive and straightforward
<br />manner.
<br />Source control of ARD using chemical
<br />treatments is a promising approach, but
<br />must be incorporated in a comprehensive
<br />plan that includes applying the
<br />treatment during placement of was
<br />te
<br />rock and minimizing infiltration of
<br />precipitation. Consequently, the semi -arid
<br />Southwest may be a good location for
<br />this technology.
<br />HydroFacts
<br />Average annual flow of the Colorado River: 15 million acre -feet
<br />Storage capacity of Colorado River reserv
<br />oir system: 60 million acre -feet
<br />Water in storage as of December 2004: about 35 million acre -feet
<br />Low reservoir level impact on hydropower production, Hoover Dam, 2003 -1993: -15%
<br />Low reservoir level impact on hydro
<br />power production, Glen Canyon Dam, 2003 -1993: -30%
<br />Cost to build Hoover Dam Visitors' Center, 1992 -1995: over $100 million
<br />Cost to build Hoover Dam, 1930-1935:
<br />$49 million
<br />Cost to build Hoover Dam in 1933, adjusted for inflation to 1993 -4 dollars: $550 million
<br />Total Dissolved Solids, Colorado River headwaters: 70 mg /liter
<br />Total Dissolved Solids, Colorado River at U.S.-Mexico
<br />border: 800 mg /liter
<br />March /April 2005 •Southwest Hydrology • 11
<br />■ DicaI +SCN
<br />Reduction in ARD parameters after 19 weeks by combined
<br />phosphate and thiocyanate treatment of sulfidic waste rock in
<br />laboratory humidity cell tests. P rock + SCN = phosphate rock
<br />plus thiocyanate treatment, Dical + SCN = agricultural (more
<br />soluble) phosphate plus thiocyanate treatment.
<br />and phosphate treatment dramatically
<br />reduced ARD production (see chart
<br />above) by controlling both chemical
<br />and biological oxidation of sulfides.
<br />Thiocyanate improves the stability and
<br />longevity of iron phosphate coatings and
<br />precipitates because it stops microbially
<br />catalyzed reactions that generate extremely
<br />acidic conditions.
<br />Field performance, however, is the
<br />key criterion of success. Researchers
<br />began tests in summer 2004 at the Red
<br />Dog zinc -lead mine in northwestern
<br />Alaska to evaluate whether thiocyanate
<br />and phosphate can control oxidation of
<br />sulfides in waste rock. The waste rock
<br />contains zinc sulfide and pyrite as the
<br />primary sulfide minerals. Waste rock
<br />in 600 -ton lined test pits was dosed
<br />with combinations of thiocyanate and
<br />phosphate. It was then leached with
<br />rainfall and snowmelt only. Results from
<br />the first season showed that following
<br />initial washout of soluble salts, leaching
<br />of ARD parameters using the combined
<br />treatment was reduced 50 to 70 percent
<br />compared to untreated rock. The test will
<br />continue next year.
<br />The cost of the combined treatment is
<br />about $1 per ton of waste rock but can
<br />be further reduced if phosphate rock is
<br />found to be effective and practical at large
<br />scales. This cost is much lower than other
<br />proposed source control technologies. Key
<br />questions being addressed in field trials
<br />are longevity of the treatment, the most
<br />effective forms and dosages
<br />of thiocyanate and phosphate,
<br />and the best methods of
<br />application.
<br />Although thiocyanate and
<br />phosphate are relatively
<br />benign, releasing them
<br />into receiving waters in
<br />elevated concentrations is
<br />undesirable. The preferred
<br />approach to ARD control is
<br />to minimize the use of these
<br />chemicals, thereby avoiding
<br />their presence in seepage or
<br />drainage. Drainage or seepage containing
<br />these chemicals can be recycled or treated
<br />using active or passive processes in a
<br />relatively inexpensive and straightforward
<br />manner.
<br />Source control of ARD using chemical
<br />treatments is a promising approach, but
<br />must be incorporated in a comprehensive
<br />plan that includes applying the
<br />treatment during placement of was
<br />te
<br />rock and minimizing infiltration of
<br />precipitation. Consequently, the semi -arid
<br />Southwest may be a good location for
<br />this technology.
<br />HydroFacts
<br />Average annual flow of the Colorado River: 15 million acre -feet
<br />Storage capacity of Colorado River reserv
<br />oir system: 60 million acre -feet
<br />Water in storage as of December 2004: about 35 million acre -feet
<br />Low reservoir level impact on hydropower production, Hoover Dam, 2003 -1993: -15%
<br />Low reservoir level impact on hydro
<br />power production, Glen Canyon Dam, 2003 -1993: -30%
<br />Cost to build Hoover Dam Visitors' Center, 1992 -1995: over $100 million
<br />Cost to build Hoover Dam, 1930-1935:
<br />$49 million
<br />Cost to build Hoover Dam in 1933, adjusted for inflation to 1993 -4 dollars: $550 million
<br />Total Dissolved Solids, Colorado River headwaters: 70 mg /liter
<br />Total Dissolved Solids, Colorado River at U.S.-Mexico
<br />border: 800 mg /liter
<br />March /April 2005 •Southwest Hydrology • 11
<br />
|