Papers by Keyword: Phosphogypsum (PG)

Abstract: By using XRD、SEM and other experimental methods, some details of polycarboxylate superplasticizer on the hydration products and performance of phosphogypsum-based cement(PBC) can be obtained. It can be found that the polycarboxylate superplasticizer makes the structure of the cement stone more compact, and significantly increases the strength of the cement. Besides, it can also improve the anti-carbonation and degradation properties of that cement.

Abstract: The effect of phosphogypsum (PG) modified on mechanical properties of super sulphate cement (SSC) was systematically studied in this paper. Then attentions and researches were focused on the relationship between specific surface (SSA) and the mechanical properties of SSC containing PG modified by calcining, floating, neutralizing with alkali. Strengthening mechanisms of SSC were further investigated and analyzed by laser particle size analyzer and chemical composition analyzer at last. Results showed that the high strength SSC with the compressive strength 35MPa at 7 days, over 60MPa at 28 days, and some even more than 70MPa at 56 days, could be successfully developed. This research can provide a key reference for the utilization of PG and development of high performance eco-SSC.

Abstract: The effect of different additives on thermal decomposition of phosphogypsum was investigated by means of a thermogravimetry coupled with a Fourier transform infra-red spectroscopy. These additives included C, CaO, Al₂O₃ and S. The temperature of thermal decomposition of phosphogypsum is about 1100~1320°C without any additives under the background of nitrogen. The temperature of the thermal decomposition of phosphogypsum decreased obviously with the addition of CaO, C and S. No influence was found for the thermal decomposition of phosphogypsum with the addition of Al₂O₃. As one of evolved products from the thermal decomposition of phosphogypsum, SO₂ production was discussed.

Abstract: Phosphogypsum is the gypsum as a byproduct. It caused serious environment pollution. In this study, leaching As of phosphogypsum was studied by leaching equipment of self-made. We get some results of As heavy metals of the phosphogypsum affect the soil. The results show that: the content of arsenic is increasing and the pH of the soil is gradually decreased with the increasing of the leaching time. Different leaching velocity will cause different the content of arsenic of the soil.

Abstract: Modern concrete is now common to use admixture (chemical or mineral), pozzolana’s for modifying different properties of concrete in fresh and hardened state. This paper presents the salient features of the development of Phosphogypsum(PG) Cement Concrete and discuss the improvements affected in the properties of concrete with the use of PG as an admixture compared to the plain or conventional cement concrete. This was accomplished by an experimental study by preparing different grades of cement concrete mix M20, M25 and M30 using PG as an admixture by replacing 5% of OPC and few durability parameters were investigated. This includes studying the compressive strength, workability, air entrainment and moisture movement by wetting and drying method. Study were conducted for modifying the properties of the concrete, controlling the concrete production cost, to overcome the scarcity of cement, and finally the advantageous disposal of industrial wastes.

Abstract: Non-fired load-bearing wall brick was prepared utilizing non-treated original waste PG as raw material in the laboratory. When the amount of PG and cement is 65% and 10% (by weight) in the brick mixture, respectively, the compressive strength of bricks is still over 23MPa and the flexural strength comes up to 4MPa. Besides, the bricks hold excellent water-resistance and frost-resistance. Effects of steel slag or/and fly ash content on performance of bricks and effects of the change of sand content on water-resistance and frost-resistance are discussed. Results indicate that the compressive strength, flexural strength and soft coefficient are higher when blended mineral additive with various amounts of steel slag and fly ash. The frost-resistance goes up with the increase of the steel slag content, the water-resistance and frost-resistance goes down when the sand content decreases from 15% to 10%, no matter the 5% sand was replaced by fly ash or steel slag as equal weight. Microstructure of brick was investigated by XRD and SEM. Strength of brick results from a large amount of AFt (3CaO•Al2O3•3 CaSO4•32H2O) and C-S-H (calcium silicate hydrate) presented in the matrix which may be viewed as the biggest strength contributors bonding the gypsum and quartz together to a compact matrix.

Abstract: Influence factors of co-crystallized (lattice) P₂O₅ were investigated from the dihydrate process conditions and aimed to optimize the process conditions and reduce the co-crystallized (lattice) P₂O₅ content in phosphogypsum. It is found that: 1) reaction temperature, P₂O₅ concentration in liquid phase and SO₃ concentration in liquid phase are main factors influencing the content of co-crystallized (lattice) P₂O₅; 2) increasing the reaction temperature, can reduce the supersaturation ratio of the crystallization, decrease the solution viscosity, which help ions diffusion and reduce the content of co-crystallized (lattice) P₂O₅; 3) improvement of SO₃ concentration in liquid phase can increase the collision probability between calcium sulfate lattice and SO₄^2-, reduce the Ca²⁺ concentration and prevent the dissociation of phosphoric acid, so HPO₄^2- concentration does not increase, thereby reducing content of co-crystallized (lattice) P₂O₅; 4) increasing the P₂O₅ concentration in liquid phase will lead to a corresponding increase of the HPO₄^2- concentration, solution viscosity increasing, diffusion problems, and deterioration of crystallization conditions, which increased the content of co-crystallized (lattice) P₂O₅; 5) the formation mechanism of co-crystallized (lattice) P₂O₅ is: any changes in the reaction system whatever can make the local concentration or average concentration of Ca²⁺ and HPO₄^2- in the solution increased, will increase the probability of the formation of co-crystallized (lattice) P₂O₅.

Abstract: In this work, the solubility of phosphogypsum(PG) in water and saturated lime solution was determined in experiments carried out at different temperatures from 10 to 50°C. The solubility of natural gypsum(NG) was also studied at an attempt to find out differences in solubility between PG and NG due to the effect of impurities. The results show that in pure water media, PG dissolves more rapidly than NG at early time, and then equally with NG. With increasing the temperature of water, the dissolution rates PG decreased while that of NG increased. In saturated lime solution, compared with NG, the solubility of PG was distinctly influenced due to the existence of impurities. Possible reaction among soluble impurities and calcium ion retarded the dissolution of calcium sulfate dihydrate.

Abstract: This paper presents the rehydration performance of binary binders made with dehydrated cement paste (DCP) and phosphogypsum (GP). DCP was obtained by thermal treatment of hardened cement pastes in which the initial water to cement ratio was 0.5. DCP we mixed with phosphogypsum (PG) to prepare the binary binders . The effect of PG on the physical and mechanical properties of the binary binders was investigated. Scanning electron microscope (SEM) was used to indentify the structural characteristics of the rehydration products. The results showed that the setting time was prolonged and the compressive strength increased slightly by mixing DCP with PG. Microstructural observations indicated that an remarkable amount of ettringite intergrows with the hydrated calcium silicate to form a network structure. Thus, the addition of phosphogypsum can not only utilize the industrial by-product, but enhances the hydraulic properties of the DCP.

Abstract: Stabilized soil is widely used as road base and sub-base materials, and is sometimes used as covering for waste matter in China. In soil stabilization, the property of a locally available soil are usually modified though chemical stabilization[1]. Cement stabilization and lime stabilization are the two most commonly used methods. Lime-fly ash stabilized soil has been widely applied in road engineering due to its good integrity, great bearing capacity, high stiffness, and water-proofing quality[2-4]. One disadvantage of lime-fly ash stabilized soil is that without any additives, its inherent low initial strength makes it inappropriate for use under low-temperature conditions. Researchers have found that the pozzolanic reactivity among lime, fly ash, and soil contributes to the strength of lime-fly ash stabilized soil. To increase the initial strength of lime-fly ash stabilized soil, many approaches have been used to accelerate the pozzolanic reaction. Sulfate activation is one of the methods that has been widely investigated, specifically, Na2SO4 and CaSO4[5]. PG, another sulfate, has also been investigated. However, existing studies have limited to the investigation of the development of strength of the stabilized soil as road base and sub-base materials. The effect of PG on the durability of stabilized soil has rarely been implicated. This work aims to study the effect of thermally treated PG (400°C) on the properties of durability, in addition to other aspects, of lime-fly ash stabilized soil. Lime-fly ash stabilized soil with different proportions of calcined PG were prepared and cured at normal conditions for 7 d and 28 d. Mass loss and strength loss under different treatments were determined. X-ray diffraction(XRD) patterns and scanning electron microscopy(SEM) photos were examined to gauge whether improvements in the performances of the stabilized soil can be obtained by use of thermally treated PG.