Chemistry: analytical and immunological testing – Geochemical – geological – or geothermal exploration – For petroleum oils or carbonaceous minerals
Reexamination Certificate
1999-07-23
2001-11-20
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Geochemical, geological, or geothermal exploration
For petroleum oils or carbonaceous minerals
C436S025000, C436S026000, C436S028000, C436S029000
Reexamination Certificate
active
06319717
ABSTRACT:
BACKGROUND OF THE INVENTION
Acreage to undergo surface coal mining requires a permit to ensure that mining will not create an environmental waste drainage problem. The site must be tested using an acid-base accounting (ABA) method for prediction of post mining water quality. Current methods may overestimate the potential acidity or alkalinity depending on the components present in the overburden. Needs exist for the development of an improved ABA method for analysis of coal mine overburden. U.S. Pat. Nos. 5,204,270 and 5,285,071 are incorporated herein by reference.
The existing methods compare total potential acidity and alkalinity. If the comparison shows an expected acid drainage, the mine is not permitted to be established.
The current acid accounting method involves prediction of total acidity based on analysis of the total sulfur content and assumes that all sulfur will be converted to sulfate with a corresponding production of acid.
The present base accounting method involves prediction of total alkalinity based on analysis of total carbonate and assumes that the neutralizing effect of all carbonates will be realized.
Recent work has been completed to compare “improved” variations of wet chemical back titration methods to obtain a neutralization potential for mine overburdens. These methods were evaluated in a recent journal article “Neutralization Potential of Overburden Samples Containing Siderite” by J. Skousen et al. in the Journal of Environmental Quality, Volume 26, no. 3, May-June, 1997 which compared the results of 31 samples all analyzed by three different laboratories. The methods include (1) the Sobek method, (2) a method where the sample is boiled for 5 minutes, (3) a method similar to (2) but includes a filter step and treatment with hydrogen peroxide before back titration, and (4) a modified Sobek method that includes the addition of hydrogen peroxide after the first hand titration. The results showed wide variation in neutralization potential among the four methods used and among the three laboratories producing the results. Clearly, a better method is required and will be welcomed by the agencies requiring these tests.
All sulfur forms in overburden do not contribute to acidity upon weathering. Predicting acidity based on the total sulfur content may result in a higher value than the real acidity, denial of many mining permits, and the loss of jobs.
All metal carbonates found in overburdens do not contribute to an overall neutralizing effect of acids. Use of total carbonate content may overestimate the overburden neutralizing capacity. This has resulted in mining permits being denied in cases where the acidity/alkalinity are too close to predict drainage quality. A better ABA method may open some of this acreage for mining.
The Department of Energy (DOE) is interested in a thermal method for analysis of overburden. Work toward a method is described in a paper entitled “Evolved Gas Analysis—A Method for Determining Pyrite, Marcasite, and Alkaline Earth Carbonates” by Hammack in Proceedings: 204
th
National Meeting of the ACS, Wash. D.C., Aug. 23-28, 1992 and a paper entitled “Evolved Gas Analysis—A New Method for Determining Pyrite, Bicarbonate, and Alkaline Earth Carbonates by Hammack in Proceedings of the Eighth Annual West Virginia Surface Mine Drainage Task Force Symposium, Apr. 7-8, 1987. Under those conditions any siderite (iron carbonate) present would have decomposed with the calcite (calcium carbonate) and dolomite (calcium magnesium carbonate). The work did not include siderite. However, the papers did show overlap between the decomposition temperatures of rhodochrosite and calcite.
The new thermal approach, described in this application, is being used to analyze some overburden samples that are of interest to Hammack at the DOE Federal Energy Technology Center.
SUMMARY OF THE INVENTION
The invention provides a new ABA one-step thermal analytical method. The amount of sulfur dioxide produced from an overburden sample as each sulfur form is thermally oxidized or decomposed is correlated with the leachable acid content. The carbon dioxide evolving from decomposition or oxidation of each carbon form in the overburden sample is determined from the same experiment and correlated with alkalinity.
Only the sulfur forms known to contribute to leachable acidity and the carbon forms contributing to overall alkalinity are compared to determine potential acidity/alkalinity of overburden. This invention results in a significantly improved ABA method for mine overburden material. Various thermal instrument manufacturers may modify instruments to use the new method.
The inventor's previous two patents relate to development of a Controlled-Atmosphere Programmed-Temperature Oxidation (CAPTO) instrument/method for use as a tool to facilitate optimization of parameters for coal analyses, new coal upgrading technologies under study, and to solve challenging analytical problems that arise in the coal and a variety of other industries. CAPTO is used to characterize the thermal oxidation of mineral sulfides and decomposition of sulfates and carbonates. The work is modified to include siderite and rhodochrosite along with calcite and dolomite. This work has led to an inexpensive method capable of predicting the acid and base content being leached from mine overburden samples. Using a 3% oxygen/97% inert gas mixture and one determination per sample, the invention identifies the sulfur forms and the carbonates as a route to quantitatively predict the acid/base potential of the overburdens.
The present invention is important. The normal neutralization potential (for carbonate) and sulfur forms acidity predictions (for pyrite and sulfate) may overestimate the base/acid accounting for an overburden sample. Actual leaching tests that may provide a reliable prediction of the acidity/basicity to be realized from an overburden sample require a lengthy leach period (approximately 10 weeks) and cost approximately 3-4 times as much as the thermal method described below. However, no standard leaching reference method has been established, possibly due to the cost of the analyses.
Understanding the characteristics of thermal oxidation/decomposition of sulfides/sulfates-carbonates leads to a better estimate of the acidic/alkaline weathering potential of strata. This application permits a more accurate prediction of acidic mine drainage from the overburden and enables mine operators to plan their mining and reclamation operations accordingly. The test results for acid discharge potential that now must accompany each new mine permit application tend either to overestimate the acidic/alkaline potential of strata above and below the coal bed or require lengthy real-time leach analysis.
The total carbonate content of an overburden sample that contains transition metal carbonates such as iron or manganese carbonates and alkaline earth metal carbonates such as calcium carbonate and dolomite are not realized in an actual leaching experiment since only the calcium carbonate and dolomite readily leaches or contributes to an overall neutralizing effect of acids. Likewise, if an overburden that contains pyrite, iron sulfate, and calcium sulfate were analyzed for sulfur content and related to acidity, the potential acidity would be overestimated, since calcium sulfate contributes little to potential acidity.
If the total inorganic sulfur content and, therefore, the potential acidity is high in an overburden sample, a mining permit may not be issued without extensive and expensive leaching studies. However, if much of the sulfur is present as calcium sulfate, only a fraction of the potential acidity will be realized and the mine could have been permitted. Similarly, if the potential basicity is greater than the potential acidity a mining permit may be issued. However, if much of the carbonate present occurs as iron or manganese carbonate, a mine acid drainage problem may arise since most of the carbonate neutralization potential from these carbonates will not be realized.
The thermal analyt
Creighton Wray James
Gakh Yelena
Narasimhan Meera P.
Warden Jill
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