Evaluation of soil analytical methods for the characterization of alkaline Technosols: I. Moisture content, pH, and electrical conductivity
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Applying standard soil analytical methods to novel soil materials, such as tailings or soils with unusual properties, should be done with caution and with special consideration of potential interferents and possible pretreatments. The aim of this study was to investigate the effects of common variations in methods on calculated total moisture content, pH, and electrical conductivity (EC) of saline alkaline soil materials.
Materials and methods
Bauxite residue (an alkaline, saline–sodic Technosolic material) as well as two saline alkaline soils from coastal and lacustrine environments were dried under various temperatures and atmospheres, and then analyzed for pH and EC at various soil–solution ratios over time.
Results and discussion
Calculated moisture content of all samples increased with drying temperature. Dehydration of gypsum elevated calculated moisture content. Decreases in soil–solution ratio decreased suspension EC and pH in highly alkaline samples. The pH and EC of soil/water suspensions generally rose with equilibration time for bauxite residue; stable values were attained within 24–120 h. Atmospheric carbonation substantially decreased the pH of samples dried at lower temperatures.
Variations in temperature, time, and atmosphere during drying of highly alkaline and saline soil materials influenced calculated moisture content as well as chemical properties such as pH and EC. A drying temperature of 40 °C and drying to constant weight is recommended to minimize these effects. Soil–solution ratio, equilibration time, and sample preparation conditions influenced observed pH and EC, and should be standardized if attempting to compare results between studies.
KeywordsAnalytical methods Bauxite residue Pedogenesis Sample preparation Tailings Technosols
Bauxite residue mud
Carbonated bauxite residue mud
Bauxite residue mud amended with 5 % wt gypsum
Bauxite residue sand
Bauxite residue sand amended with 5 % wt gypsum
Saline alkaline clay
Saline alkaline sand
The authors wish to thank the Western Australian Department of Environment and Conservation for site access to sample the saline alkaline soils and Alcoa of Australia Limited for supplying bauxite residue used in this study. Financial support for this work was provided by Alcoa of Australia Limited and BHP Billiton Worsley Alumina and by a Minerals and Energy Research Institute of Western Australia scholarship to the senior author.
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