A simple model for rapid gypsum determination in arid soils

Abstract

The development of a reliable, fast and inexpensive method to determine the gypsum content in soils to understand their behavior is crucial. However, current methods of determination are cumbersome, lengthy and imprecise. This study was conducted to develop a rapid and simple method to determine soil gypsum content. A gypsum content of 120 soil samples was determined by three methods; (1) standard silica-gel; (2) acetone; and (3) the proposed method (OMRAN GypSim). These methods were further tested for the recovery of known amounts of pure gypsum (over the range of 0–100%). The proposed method estimates the gypsum content of water loss in the soil sample by heating at 70 °C and 135–150 °C. Sandy and clay minerals mixed with gypsum reagent powder (over the range of 0–100% gypsum) were used as a reference. Gypsum (CaSO4·2H2O), after heating at 150 °C, dehydrates, losing the two water molecules and becoming mostly anhydrite (CaSO4). The crystal water of gypsum is not lost when the gypsum is dried at 70 °C for 45 min., whereas it is lost when the gypsum is heated at 150 °C for 15 min. The reproducibility of the proposed method is worth highest (average 0.10) followed by silica-gel (average 0.35) and acetone (average 0.47). This simple, yet effective methods determined gypsum content to within 1%, whereas other methods exceeded gypsum content by as much as 10%. An easy-to-use graphical user interface has been designed for the model running in a user-friendly way.