Urban soils polluted with heavy metals are of increasing concern because it is greatly affecting human health and the ecological systems. Hence, it is mandatory to understand the reasons behind this pollution and remediate the contaminated solid. The removal of heavy metals from contaminated soil samples collected from the vicinity of the sewage lake in Jeddah, Saudi Arabia, was explored. The leaching process was studied kinetically and thermodynamically for better understanding of the remediation process. The results showed that the soil samples were slightly basic in nature, and tend to be more neutral away from the main contaminated sewage lake area. The total metal content in the soil samples was measured using the aqua regia extractions by ICP-OES and the results showed that many of the heavy metals present have significant concentrations above the tolerable limits. In general, the metal concentrations at different sites indicated that the heavy metal pollution is mainly due to the sewage discharge to the lake. The results showed excellent correlation between the concentrations of Co, As, and Hg with the distance from the main contaminated area. The leaching of Co, As, and Hg using 1.0M hydrochloric acid from the soil was studied kinetically at different temperatures and the experimental results were fitted using different kinetics models. The experimental data were best described with two-constant rate and Elovich equation kinetic models. Also, the thermodynamic study showed that the leaching process was spontaneous, endothermic and accompanied with increase in the entropy. In general, the polluted soil could be remediated successfully from the heavy metals using the acid leaching procedure in a short period of time

This study focuses on using a facile method for the green preparation of activated carbon (AC) from palm tree fiber (PTF) waste. The synthesized cost-effective AC was investigated for the removal of an anionic dye (Congo red, CR) and a cationic dye (Rhodamine B, RhB) from wastewater. The morphological and structural characterization of the synthesized AC were performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), surface area, Fourier transform infrared spectroscopy (FTIR), total pore volume, average pore diameter and pore size distribution, zeta potential, and zero-point charge. To investigate the adsorption efficiency, different parameters such as adsorbent dosage, solution pH, initial dye concentration, and duration were applied using the batch experiments. Various adsorption isotherm and kinetics models were applied to study the adsorption mechanism and dynamics. The results showed that chemical activation with a weak acid (H₃PO₄) at 400 °C for 30 min is a fast method for the activation of each precursor and produces a high yield. The result of analysis showed an increase in the adsorption capacity at pH 2. The maximum adsorption capacity was 9.79 and 26.58 mg g⁻¹ at 30 min for CR dye and RhB dye, respectively. The optimum adsorbent dosage for the activated carbon from palm tree fiber (PTFAC) was 0.15 g with a high percentage removal of CR (98.24%) and RhB (99.86%) dyes. The adsorption isotherm and kinetic studies were found to be favorable and feasible for assessing the adsorption of dyes with the Langmuir model and pseudo-second-order reaction, respectively. In addition, the AC showed reusability up to five cycles. The results showed that the synthesized AC was environmentally friendly and successfully removed dyes from wastewater.