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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/10117

Title: Nature and Composition of Newly Formed Precipitates in Relationship to Characteristics of Groundwater in Arid Environment
Authors: A. S..Sheta
M. S. AI-Sewailem
A. Sh. Sallam
A. S. Al-Mashhady
Keywords: Arid Soil Research and Rehabilitation
Issue Date: 2000
Abstract: Chemical characteristics of ground,l;ater and the composition of newly formed pre¬cipitates are critical in the managemeni of modern irrigated agriculrure in arid regions. Water samples representing the main aquifers in Riyadh region, Saudi Arabia, and solid samples from the newly formed precipitates were stUdied. Results showed that water temperature varied between 30.3-69°C. being higher in the deep aquifer and low in the relatively shallow aquifers. Initial water pH ranged from 6.39-7.92, increasing to 7.65-8.20 at atmospheric conditions. Shallow aquifer waters were categorized into sulJate-type and Cl- or no-dominant type waters, while the deep aquifers were characterized as Cl-type and no-dominant type. Soluble H4Si04, soluble Fe and Mn ranged from 3.15 to 18.82, 0.10 to 1730, and 0.01 to 0.32 mg L-1 respectively. Calculation of saturation indices from water composition at initial, closed and equilibrium conditions indicated that changes in pH and water temperature cause major chemical changes in the water far:oring the precipitation of carbonates and Fe-silicates. Data of total chemical analysis indicated that carbon-ates are present in all samples and constituted up to 976 g kg-1 of the precipitates formed from the deep aquifer water in the irrigation tubes. Amorphous and/or crys¬talline Fe compounds were the dominant fractions in the surface crust precipitates, while crystalline Fe compounds was the dominant form in the precipitates in irriga¬tion tubes and in the cooling reservoir. XRD data confirmed that aragonite was the dominant carbonate mineral in the precipitates formed from the deep aquifer water. Calcite and Mg-calcite were detected in considerably low quantities. Poorly crys¬talline Fe-oxide minerals were present i/1 all the precipitate samples. Results sug¬gested that formation of precipitates either in cooling reservoirs or in irrigation systems can be minimized by controlling the degassing through keeping the system closed, lowering the pH through the injection of inorganic acids in the system or both.
URI: http://hdl.handle.net/123456789/10117
Appears in Collections:College of Foods And Agricultural Science

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