Shear Strength Parameters of Improved Peat by Chemical Stabilizer.

The present research aimed to discuss the applicability of cationic grouts in geotechnical engineering. The effects of several cationic stabilizers such as monovalent (sodium silicate), divalent (calcium oxide and calcium chloride), and trivalent (aluminum hydroxide) were investigated on shear strength improvement of tropical peat samples. The unconfined compressive strength (UCS) tests were performed after the time frame of 7, 21, and 30 days as curing time, respectively. Apart from the physicochemical characteristics of the stabilized peat, scanning electron microscopy and energy-dispersive X-ray spectroscopy tests were also carried out to study the ongoing microstructural changes. It is to be noted that the shear strength values for peat samples rose to 8, 6, 6, and 4 % of sodium silicate, calcium oxide, calcium chloride, and aluminum hydroxide, respectively. The highest observed UCS outcome is the one taken from the calcium oxide where the UCS of treated peat after 30-day curing time increased to 76 kPa. The strength changes resulted from the various cationic stabilizers can best be explained via the consideration within the mineralogical composition as well as those physicochemical changes happening in the peat

Effect on pH of heavy metals retention by kaolinite

Heavy metals are naturally present in soils but in high concentrations they can be hazardous to the environment and human health. To understand the adsorption of the metals, Batch tests were conducted to measure the adsorption of 1, 2 and 3 mM/L concentrations of cadmium, lead and zinc onto kaolinite over periods of 0.1, 1, 2, 4, 8, 12 and 24 hours and to measure the change in hydrogen ion concentration. The kaolinite was found to contain iron oxides which increased the point of zero charge of the kaolinite to pH 4.7 and the pH 7 CEC to 17.8 meq/100 g. The clay retained a maximum of 10 μM/g of lead, 8.4 μM/g of zinc and 6.0 μM/g of cadmium. Similar adsorption behaviours were found for Pb and Zn, while Cd shows a different trend. The pH of the solution highly influences the adsorption of Cd but it has little effect in the adsorption of the other two metals. Among the three metals Pb was present the slowest adsorption at 0.1 hrs. From the kaolinite reactive spaces, the aluminium hydroxyl, silicon oxide and iron oxide sites are probably involved in the release or retention of hydrogen ions. The ratio of hydrogen ions released to metal adsorbed is presented and the trend for each metal is examined with their respective equations. In addition, the desorption for the 1 mM/L concentrations of the three metals is examined. Adsorption isotherms are used to help analyze the adsorption data

The importance of thiosalt speciation in the management of tailing pond

The presence of thiosalts in mining wastewaters is an environmental issue due to the resulting pH depression as these species degrade with time. Despite research in the area, reaction kinetics of thiosalt species under different pH and temperature conditions are not fully understood, especially in conditions common in receiving ponds. As a result, it is difficult to design ponds or develop treatment technologies to treat these compounds. Several studies have dealt with the reaction kinetics of major thiosalt species (thiosulfate, trithionate, tetrathionate) under various pH and temperature conditions. However, further research is required to better understand the fundamental behaviors of thiosalt species and identify probable reaction paths in temperatures below 30°C, pH range between 2 and 9 and in the presence of reagents. -- The overall objectives of this work have been to study the behavior of thiosalts in mining wastewaters and develop a model of their behavior under the conditions studied that includes pH and temperature as independent variables. The study is divided in four parts: the first part is a summary of relevant information in terms of generation and kinetics of thiosalts, analytical methods for measuring their concentrations, and treatment of thiosalt wastes. Despite extensive research in the area, generation and kinetic information of thiosalt species under different pH and temperature conditions is not fully understood, especially under the range of conditions likely to be encountered in receiving ponds. -- The second part of the study analyzes the behavior of thiosulfate, trithionate and tetrathionate and provides with mathematical models for their behavior as pure species under the specified conditions. The third part of the study consists of the analysis of the thiosalt behavior in mixtures following a decoupling approach; this analysis provided with additional information for the proposal of global reaction pathways for the species. Finally, the last chapter provides preliminary results from kinetic experiments with selected reagents, results from equilibrium simulations and an analysis of future work required to improve the understanding of thiosalt reactions, improve treatment efficiency and reduce the environmental impact of acid mine drainage