A PRESENTATION ON RECLAMATION OF SALINE-SODIC SOILS BY (FGDG)

Flue gas desulfurization gypsum (FGDG) is an industrial by-product generated during the flue gas desulfurization process in coal-fired power plants.
Due to its abundance of chemical and physical properties, FGDG has been used in reclamation of saline-sodic soils.
In the recent developments of flue gas desulfurization processes, the “modern” FGDG contains lesser amounts of heavy metals, thus increasing its efficiency and beneficial value.

1. Dept. of Soli Science And Agricultural Chemistry Bihar Agricultural College, B.A.U. Sabour A PRESENTATION ON RECLAMATION OF SALINE-SODIC SOILS BY (FGDG) Presented By:- Chandni Rani M-SSAC-00758-BAC-2020-21 Dept. of Soli Science And Agricultural Chemistry

2. INTRODUCTION

3. ABOUT FGDG METHODOLOGY Flue gas desulfurization gypsum (FGDG) is an industrial by-product generated during the flue gas desulfurization process in coal-fired power plants. Due to its abundance of chemical and physical properties, FGDG has been used in reclamation of saline-sodic soils. In the recent developments of flue gas desulfurization processes, the “modern” FGDG contains lesser amounts of heavy metals, thus increasing its efficiency and beneficial value.

4. WHAT IS FLU GAS DESULPHURIZATION PROCESS? Flue-gas desulfurization (FGD) is a set of technologies used to remove  sulfur dioxide  (SO 2 ) from  exhaust flue gases of fossil-fuel power plants , and from the emissions of other sulfur oxide emitting processes such as waste  incineration . In a flue gas desulphurization system (FGD),  Sulphur compounds are removed from the exhaust emissions of fossil-fueled power stations. This is done by means of an industrial process through the addition of absorbents. In this method, the flue gases are steam-saturated with the absorbent in aqueous solution.

5. HOW FGDG WORKS IN SODIC SOILS? The application of FGD-gypsum is an established technique to remediate saline-sodic soils. FGD-gypsum, as a major by-product of coal-fired power plants, is widely used as a chemical amendment to supply Ca2+ to offset Na+ on soil exchange sites. The reclamation of saline-sodic soil requires leaching of desorbed Na+ from soil exchange sites into soil solution by divalent cations (usually Ca2+) to facilitate soil flocculation, with subsequent leaching to drain salts from the soil profile. The application of FGDG, which provide Ca2+ ions to replace the exchangeable Na+ ions .

6. CHEMISTRY OF FGD GYPSUM FORMING PROCESS An overall chemical reaction of the processes, which occurrs in the FGD system is given below:- SO2(g) + CaCO3(s) + 2H2O(aq.) = CaSO3·2H2O(aq.) + CO2(g) The produced calcium sulfite (CaSO3·2H2O) is then oxidized, resulting in FGDG. CaSO3·2H2O(aq.) + ½O2(g)↔CaSO4·2H2O(s) Natural oxidation processes may occur in desulfurization systems, depending on the pH of the limestone slurry, and the SO2 and excess air content of the flue gas. In this case, a mixture of CaSO3·½H2O and CaSO4·.2H2O is produced as the by-product. But, under forced oxidation CaSO4.2H2O is dominant (> 90%). limestone (CaCO3) and lime ( CaO ) are used as Ca(OH)2 sources and available at low cost.

7. HOW FGDG RECLAIMS THE SALT AFFECTED SOIL SOIL When FGDG applied to salt affected soils,the following reactions will take place and loss of exchangeable sodium(Na+) occurs while calcium takes place of sodium in the exchange soil complex. FGD Gypsum reacts with both Na2Co3 and the adsorbed sodium. Na2Co3 + CaSo4 CaCo3+Na2So4 ( leachable) Clay]2Na+ + Caso4 Ca[clay]+ Na2so4 ( leachable)

8. ADVANTAGES OF FGDG IN SALINE SOIL RECLAMATION In recent years, FGD-gypsum as a saline-soil amendment is very popular for its low cost, large output and fast repair rate. FGD-gypsum improves saline-soil which is native to mineral gypsum, where calcium ions promotes the aggregation of clay particles and displace excess of sodium ions from the soil colloids. Compared with mineral gypsum, FGD-gypsum has better physical and chemical properties and economic effects, such as finer particles, higher solubility, higher purity, greater production, lower cost and so on. FGD-gypsum accelerate soil saturated hydraulic conductivity.

9. LIMITATIONS Although flue gas desulfurization (FGD) gypsum has become an effective soil amendment for sodic soil reclamation, it carries extra heavy metals like Arsenic, mercury, sel enium, lead e.t.c . which contaminates the soil environment. The fate of heavy metals introduced by FGD gypsum in sodic or saline–alkali soils is still unclear. The reclamation of saline–alkali or sodic soils using FGD gypsum may contaminate the soils with these heavy metals. FGD gypsum greatly reduced the exchangeable Na, K, and Mg cation concentrations in the sodic soils. The concentrations of As and Cd increased with depth in the soil columns upon leaching, while the Pb and Hg concentrations decreased due to the differences in their mobility.