A Study On Use Of Phosphogypsum Neutralized By Lime Mixed Selected Alkali Industrial By Products And Geosynthetic Clay Liner In Composite Base Lining System Of Phosphogypsum Ponds

Abstract

The disposal of phosphogypsum, a byproduct of phosphoric acid production and fertilizer manufacturing, has become an increasingly crucial environmental challenge worldwide. Phosphogypsum primarily consists of calcium sulfate dihydrate (CaSO4·2H2O) along with impurities like residual acid, heavy metals and fluoride. Due to its acidic nature and potential for leaching contaminants into subsoil, the safe containment and management of phosphogypsum are important. From a civil engineering standpoint, the unlined dumping of phosphogypsum presents a critical challenge in environmental management. When this material is disposed of without proper containment measures, such as liners, it poses a significant risk of soil contamination. The acidic nature of phosphogypsum can considerably alter soil pH, jeopardize structural integrity/longevity and suitability for construction projects. Migration of contaminants from the contaminated sites can lead to further environmental degradation, impacting nearby water bodies and complicate engineering projects that rely on clean soil and water resources. Therefore, addressing the challenges of unlined phosphogypsum dumping is of utmost importance. Proper disposal practices and the incorporation of effective containment systems are imperative to mitigate the risks. The studies on underground contamination due to the dumping of phosphogypsum without base lining system are limited. In response to these challenges, extensive laboratory research has been conducted to address the issue of soil contamination and to suggest a base lining system for phosphogypsum stacking yards. To ascertain the extent of soil contamination resulting from the disposal of phosphogypsum without liners, 3 exploratory boreholes of 150mm diameter and 10m length are made by rotary boring and subsoil samples are collected. The study showed a decrease in pH levels (lt 7) of the soil in contaminated zones. The chlorides and sulphates in soil samples determined by Ion Chromatography revealed an increase in sulphate conten