Dependence of cadmium, lead, and copper speciation on soil pH and temperature using VISUAL MINTEQ

Soil contamination by heavy metals poses a significant threat to the environment and human health, primarily due to the toxicity of these metals and their ability to accumulate in organisms. To determine how soil pH and temperature affect the chemical speciation, mobility, and immobilization potential of cadmium (Cd²⁺), lead (Pb²⁺), and copper (Cu²⁺). The main hypothesis posits that as pH increases, the concentration of free heavy metals decreases due to the formation of complexes and precipitation, whereas an increase in temperature accelerates the kinetics of chemical reactions, thereby altering metal activity. Using the Visual MINTEQ modeling tool, simulations were carried out under various pH (4–8) and temperature (15–40 °C) conditions. The results showed that at lower pH, metal activity significantly increases; however, the influence of temperature is more complex–both positive and negative trends were observed depending on the metal. These findings provide a foundation for further research, particularly for optimizing strategies to immobilize contaminated soils. Nonetheless, certain observed trends diverged from initial assumptions and called for additional investigation.