Phosphogypsum Content Research Articles

Ecological evaluation of artificial soils treated with phosphogypsum

An attempt to set up ecologically acceptable concentrations of toxic components contained in phosphogypsum was made for soils of different land uses. For this purpose, an experimental ecological evaluation of a standard soil mixture (model artificial soil ISO 11268-1) treated with phosphogypsum was performed. Both positive and negative effects of the phosphogypsum components were found. Thus, a significant increase in the biomass of lawn grasses was observed in the model soil with the phosphogypsum content of less than 3.3%. In the soil containing more than 6.8% phosphogypsum, the concentrations of Sr and F exceeded the maximum permissible values and adversely affected the living organisms. According to the basic ecological norms, the allowable content of phosphogypsum should be ≤2.0% for the soils of specially protected natural areas; ≤6.8% for agricultural and urban soils; and ≤9.6% for the soils of forest, water management, and transport lands.

РЕЗУЛЬТАТЫ ИССЛЕДОВАНИЯ ФИЗИКО-МЕХАНИЧЕСКИХ СВОЙСТВ СМЕСЕЙ ОСАДКА СТОЧНЫХ ВОД С ГРУНТАМИ И ФОСФОГИПСОМ ДЛЯ ИСПОЛЬЗОВАНИЯ ИХ В КАЧЕСТВЕ РЕКУЛЬТИВАНТОВ

The authors argue that intensive construction and development operations generate a large number of idle quarries. Now Moscow Metropolitan area has about 2,000 abandoned quarries and in excess of 150 quarries in operation. Most of them were used to develop various minerals, namely, sand, crushed stone, gravel, peat and other materials. Recovery of abandoned quarries and assurance of their safe condition requires a set of actions to be taken. However, mere reclamation cannot resolve all environmental problems arising after the completion of mining operations. Obviously, the use of undisturbed land areas as household waste landfills is not the best idea from the viewpoint of the environment. Therefore, filling idle quarries with specific types of products is an improved method of reclamation of mines and quarries. This method may solve two problems at once: they are land reclamation and safe waste disposal. Sewage sludge generated by households, as well as industrial enterprises, may serve as the solution. In this paper, the authors study the dependence between the permeability ratio, the carrying capacity of different soil mixtures containing sewage sludge to be used as the reclamation agent in the course of restoration of disturbed territories. The authors also consider dependence of concentration of biogases and the phosphogypsum content in biogases.

Compaction Characteristics and Bearing Ratio of Pond Ash Stabilized with Lime and Phosphogypsum

Recycling of waste material is one of the effective solutions of its disposal problem. Fly ash produced by coal-based thermal power plants and phosphogypsum (PG) produced by fertilizer plants producing phosphoric acid as constituent of fertilizers, take huge disposal area and creates environmental problems. Stabilization/solidification of fly ash improves the engineering properties and reduces the environmental problem like leaching and dusting. This paper presents the laboratory test results of a Class F pond ash alone and stabilized with varying percentages of lime (4, 6, and 10%) and PG (0.5, and 1.0), to study the suitability of stabilized pond ash for road base and subbase construction. Standard and modified Proctor compaction tests have been conducted to reveal the compaction characteristics of the stabilized pond ash. Bearing ratio tests have been conducted on specimens, compacted at maximum dry density and optimum moisture content obtained from standard Proctor compaction tests, cured for 7, 28, and 45 days. Both unsoaked and soaked bearing ratio tests have been conducted. This paper highlights the influence of lime content, PG content, and curing period on the bearing ratio of stabilized pond ash. The empirical model has been developed to estimate the bearing ratio for the stabilized mixes through multiple regression analysis. Linear empirical relationship has been presented herein to estimate soaked bearing ratio from unsoaked bearing ratio of stabilized pond ash. The experimental results indicate that pond ash-lime-PG mixes have potential for applications as road base and subbase materials.

The using of waste phosphogypsum and natural gypsum in adobe stabilization

The best known disadvantages of adobe are its low mechanical properties and poor resistance to water damage. In this research waste phosphogypsum (PG) and natural gypsum were used as stabilization material to improve the properties of adobe soil and to reduce its disadvantages at least partially. The compressive and flexural strength, softening in water, drying shrinkage and unit weight values were determined on adobe samples. The strength values of adobe samples increased with both gypsum additions. The most resistance of the adobe samples against softening in water was obtained with 25% PG addition. Drying shrinkage of test samples reduced with increasing PG content. The dry unit weight of the specimens was not in the recommended range specified in the standards. Test results showed that PG can be used as alternative material in adobe stabilization to bring economy and to reduce environmental pollution.

Hydration characteristics of tricalcium aluminate phase in mixes containing β-hemihydate and phosphogypsum

The tricalcium aluminte phase was prepared from pure chemicals on a laboratory scale. Five mixes were formulated from the prepared C 3A phase, β-hemihydate, phosphogypsum, calcium hydroxide and quartz. Different mixes were hydrated at various time intervals, namely, 6, 24, 72 and 168 h. The kinetics of hydration was measured from chemically combined water and combined lime contents. The phase compositions and microstructures of the hydrated products were studied by X-ray diffraction (XRD), differential thermal analysis (DTA)/TG, scanning electron microscopy (SEM) techniques and FT-IR spectroscopy. This work aimed to study the effect of partial to full substitution of phosphogypsum by β-hemihydate on the hydration characteristics and microstructures of tricalcium aluminte phase. The results showed that the combined lime slightly increases with the increase of amounts of phosphogypsum. The XRD patterns showed the increase in the intensities of monosulphate and different forms of calcium aluminate (C 4AH 13 and C 4AH 19) with phosphogypsum content. Ettringite is less stable than monosulphoaluminate, so it transformed into monosulpho-aluminate after 24 h, which persisted up to 168 h. The mechanism of the hydration process of C 3A phase in the presence of phosphogypsum proceeds in a similar path as with β-hemihydate. Phosphogypsum reacts with C 3A in the presence of Ca(OH) 2 forming sulphoaluminate hydrates, which are responsible for setting regulation in cementitious system.