Removal of Mercury from Aqueous Environments Using Polyurea-Crosslinked Calcium Alginate Aerogels

The removal of mercury(II) from aquatic environments using polyurea-crosslinked calcium alginate (X-alginate) aerogels was investigated through batch-type experiments, focusing on low mercury concentrations (50-180 μg·L^-1), similar to those found in actual contaminated environments. Within this concentration range, the metal retention was very high, ranging from 85% to quantitative (adsorbent dosage: 0.6 g L^-1). The adsorption process followed the <i>Langmuir</i> isotherm model with a sorption capacity of 4.4 mmol kg^-1 (883 mg kg^-1) at pH 3.3. Post-adsorption analysis with EDS confirmed the presence of mercury in the adsorbent and the replacement of calcium in the aerogel matrix. Additionally, coordination/interaction with other functional groups on the adsorbent surface may occur. The adsorption kinetics were best described by the pseudo-first-order model, indicating a diffusion-controlled mechanism and relatively weak interactions. The adsorbent was regenerated via washing with a Na₂EDTA solution and reused at least three times without substantial loss of sorption capacity. Furthermore, X-alginate aerogels were tested for mercury removal from an industrial wastewater sample (pH 7.75) containing 61 μg·L^-1 mercury (and competing ions), achieving 71% metal retention. These findings, along with the stability of X-alginate aerogels in natural waters and wastewaters, highlight their potential for sustainable mercury removal applications.