The structural and surface changes undergone by the different precursors that are produced during the synthesis of imogolite are reported. The surface changes that occur during the synthesis of imogolite were determined by electrophoretic migration (EM) measurements, which enabled the identification of the time at which the critical precursor of the nanoparticles was generated. A critical parameter for understanding the evolution of these precursors is the isoelectric point (IEP), of which variation revealed that the precursors modify the number of active ≡Al-OH and ≡Si-OH sites during the formation of imogolite. We also found that the IEP is displaced to a higher pH level as a consequence of the surface differentiation that occurs during the synthesis. At the same time, we established that the pH of the reaction (pH_rx) decreases with the evolution and condensation of the precursors during aging. Integration of all of the obtained results related to the structural and surface properties allows an overall understanding of the different processes that occur and the products that are formed during the synthesis of imogolite.

Sulfide mineral mining produces highly sulfate-contaminated wastewater which needs to be treated before disposal. A composite material was made from natural zeolite (NZ) and Superfloc^® SC-581, a polyammonium cationic polymer. The resulting modified zeolite (MZ) demonstrated improved capacity for sulfate abatement from wastewater compared to NZ. Above pH 4.0, MZ retained positive surface charge while NZ remained negative. The effect of the ionic strength on the adsorption process was evaluated. Sulfate adsorption capacity was assessed and revealed MZ to be superior to NZ in all cases. Adsorption kinetics reached equilibrium after 10–12 h, with MZ adsorption being twice that of NZ; data fitted a pseudo-second order kinetic model. Adsorption isotherms reflected the high capacity of MZ for sulfate adsorption with maximum of 3.1 mg g⁻¹, while NZ only achieved 1.5 mg g⁻¹. The process corresponds to heterogeneous partially reversible adsorption of ionic species over the solid adsorbent. Langmuir–Freundlich parameters revealed that adsorption over MZ corresponds to an interaction eight times stronger than that on NZ. The sulfate adsorption pattern changes with ionic strength. Taken together, the composite formed between natural zeolite and polyammonium represents an adsorbent that maintains the adsorption capacity of zeolite and proves suitable for anionic species removal. Further prospect considers the testing of the composite with other anionic pollutants (arsenate, phosphate, perchlorate, etc.)

The sorption behavior of 2,4-dichlorophenoxyacetic acid (2,4-D) in the abundant agricultural volcanic ash-derived soils (VADS) is not well understood despite being widely used throughout the world, causing effects to the environment and human health. The environmental behavior and risk assessment of groundwater pollution by pesticides can be evaluated through kinetic models. This study evaluated the sorption kinetics and 2,4-D sorption–desorption in ten VADS through batch sorption experiments. Differences in the sorption extent for the fast and slow phases was observed through the $\mathrm{IPD}$ model where 2,4-D sorption kinetics was controlled by external mass transfer and intra organic matter diffusion in Andisols (${\mathrm{C}}_1$ ≠ 0). We confirmed from the spectroscopic analysis that the carboxylate group directly drives the interaction of 2,4-D on Andisol soil. The MLR model showed that $IEP$, $F{e}_{DCB}$, and $pH\times Silt$ are important soil descriptors in the 2,4-D sorption in VADS. The Freundlich model accurately represented sorption equilibrium data in all cases ($K_f$ values between 1.1 and 24.1 µg^1−1/n mL^1/ng⁻¹) with comparatively higher sorption capacity on Andisols, where the highest hysteresis was observed in soils that presented the highest and lowest $OC$ content ($\mathrm{H}$ close to 0).

Environmental context. Intensive fertilisation and the availability of phosphorus species (less than 10%) in cultivable soils of volcanic origin are causing the accumulation of P in these soils. Phosphorus is a macronutrient that severely limits good agricultural development, so knowledge of the distribution and the different forms of P present in soils is fundamental for sustainable agricultural practice. This novel study reports the existence of increased available P in all the soils that received a load of plant ash from different tree species. The effect associated with the distribution of ash from plantations of native, pine, and eucalyptus forests over five soils of volcanic origin was studied by means of column leaching experiments. The results show a clear increase of pH (up to 4.4 units) and of the soil’s electric conductivity (up to 21 times), whereas total extractable P content increased 3 to 10 times with respect to the control. These effects follow a sequence depending on the origin of the ash (native forest, pine, eucalyptus), concentrated in the 0.0–10.0-cm section from the top of the columns. The observed alkalinity caused an increase of available P (from 21 to 72 times with respect to the control), in addition to decreasing residual P and increasing the extraction efficiency of the method used, discarding a transformation of inorganic P into organic P. Finally, the results show that the addition of ash is a valid and complementary alternative to phosphate fertilisation.