Gypsum applications to aggregated saline—sodic clay topsoils
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SUMMARY Gypsum application was highly efficient as a treatment for reducing amounts of exchangeable sodium and inhibiting clay dispersion in highly structured saline‐sodic clay topsoils. Phosphogypsum, applied to the surfaces of aggregates in soil columns treated with simulated rainfall, was dissolved efficiently by frequent intermittent ‘rainfall’. The calcium released by dissolution displaced sodium on the exchange complex within soil aggregates ranging from 7.5 mm to 45 mm in diameter. Of the applied calcium, 64–74% was transferred to ion exchange sites; however, almost one‐third of this adsorbed calcium displaced exchangeable magnesium. Comparison of three gypsum treatments, phosphogypsum, rock gypsum, and a saturated gypsum solution (representing a top dressing of highly soluble gypsum), showed that the effectiveness of calcium uptake on the exchange complex followed the order: rock gypsum < saturated solution < phosphogypsum, but differences were small. Application of phosphogypsum caused a 90% reduction in the total amount of dispersed clay released in column leachates, and decreased the maximum clay concentration in the effluents by at least 80%, when compared to soils leached without gypsum treatment.Keywords:
Phosphogypsum
Sodic soil
Sodium adsorption ratio
Cation-exchange capacity
Phosphogypsum of 15 million tons is being produced each year from phosphate industry and this must be disposed properly in view of economic and environmental considerations. Phosphogypsum can be made into various products such as calcined gypsum, αhighstrength gypsum powder, ornament materials (papered gypsum plank, ornamental gypsum plank, fabric gypsum plank, partition gypsum plank cement retarder, and wall body material, the usage of the above products and their manufacture are described.
Phosphogypsum
Plank
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Phosphogypsum
Beneficiation
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The wet phosphoric acid plant features large amount of by product phosphogypsum, which poses significant pollution to the environment and must be treated before comprehensive utilization. The characteristics of main types of chemical gypsums, the impact of impurities on the gypsum products, as well as the impurity's grain size distribution in the phosphogypsum is introduced. The phosphogypsum purification and gypsum calcinations processes are introduced and it is concluded that the slow calcinations and quick calcinations have their respective advantages and disadvantages, and the calcinated building gypsum powder will meet quality requirements for gypsum products.
Phosphogypsum
Phosphoric acid
Environmental Pollution
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Sodic soil
Sodium adsorption ratio
Amendment
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Gypsum binder was received by the method of intensive dehydration and the influence of admixture in phosphogypsum on the hydration process of gypsum binder was researched. Phase composition of phosphogypsum before and after calcination, using XFA, IR-spectroscopy and crystal optic analysis was defined. Dry mortar for plaster of interior walls of buildings on the basis of CaSO4·0,5H2O obtained from phosphogypsum is investigated. Its advantages and physical and chemical characteristics are shown
Phosphogypsum
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Phosphogypsum
Hemihydrate
Coprecipitation
Anhydrite
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Calcium sulfate whisker(CSW) was an excellent,low price and green materials.Since the main use of non-renewable natural gypsum as raw materials,long-term exploitation of resources would inevitably lead to depletion of gypsum.At present,China used industrial by-product production of gypsum whisker to research focuse on the progress of phosphogypsum whiskers,pointed out that the current generated in the process of WPA mountains of phosphogypsum,full use of phosphorus gypsum production gypsum whisker would be a major trend in the future,and the market had great potential.
Phosphogypsum
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The possibility of transforming phosphogypsum into calcined gypsum has been studied. The properties of phosphogypsum have been analyzed and the best technological procedure of changing phosphogypsum into calcined gypsum has been determined. By pre-treating phosphogypsum and eliminating some impurities, we can get β-type gypsum. Using this material and other additives, we produce a new phosphogypsum building plaster with higher additional value.
Phosphogypsum
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For reclaiming calcareous sodic and saline-sodic soils, various amendments like gypsum, calcium chloride, hydrochloric acid and sulphuric acid can be used. These amendments either change insoluble soil calcium to soluble form or supply calcium directly to replace the adsorbed sodium from sodic and saline-sodic soils. Out of all these amendments, gypsum is the most commonly used one due to its cheap availability in Pakistan (Ghafoor et al., 1985a, b). The fineness to which gypsum must be ground is a matter of economic consideration. Grinding to a very fine size entails higher cost, though it will give higher availability of soluble calcium to replace the exchangeable sodium. Simultaneously, the higher sodium adsorption ratio (SAR) of sodium-problem soils as well as of irrigation waters may increase the solubility of gypsum due to decreased activity coefficient (Bohn et al., 1985) which is the only its demerit. The present study was planned to see the effects of different levels of water SAR
Sodic soil
Sodium adsorption ratio
Fineness
Hydrochloric acid
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Abstract A number of various proposed options and flow charts applied for the production of gypsum binders are considered herein. Large volumes of inorganic waste amount to millions of tons therefore the phosphogypsum utilization to get effective gypsum binders is an urgent issue. The production of phosphogypsum binders both in our country and abroad is indicated to go in three main directions - burnt, autoclaved and anhydrite (hard-burnt) binders.
Phosphogypsum
Anhydrite
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