In this work, the adsorption-desorption dynamics of diuron in three typical Kenyan agricultural soils, Nzoia (NZ), Thika (TH) and Machakos (MK) was investigated. The equilibrium adsorption data, tested against three classical nonlinear adsorption isotherms, was best described by the Freundlich model. The Freundlich adsorption constant, (KF), increased in the order MK > TH > NZ soil. Additionally, the negative Gibb's free energy values indicate the adsorption processes were thermodynamically spontaneous and physical. Multiple linear regression analysis indicated that the adsorption-desorption behavior was controlled by the clay and phosphorus contents of the soil. Phosphorus negatively affected the adsorption of diuron and promoted desorption. The groundwater ubiquity score (GUS) indicated that diuron movement rating in MK soil was ‘moderate’ while the movement in TH and NZ soils was ‘high’.

Alkali-activated municipal waste incineration fly ash (MWFA)-based geopolymers (GPA, GPB, and GPC) were synthesized under different sodium silicate to sodium hydroxide (SS/SH) ratios. The geopolymers were applied in the removal of endosulfan, a persistent and toxic chemical, from water. The adsorbents were characterized by XRD, SEM-EDX, and FTIR. Variation of SS/SH ratios resulted in morphologically distinguishable geopolymers with different compositions. The adsorption equilibrium data were best described by the Langmuir isotherm. The maximum adsorption capacities increased with an increase in SS/SH ratios in the order 1.87, 15.89, 16.97, and 20.01 mg/g for MWFA, GPA, GPB, and GPC, respectively. The kinetic data were best described by the pseudo-first-order model wherein the adsorption rate (k1) was independent of the SS/SH ratios and the geopolymer composition. The thermodynamic parameters, that is, enthalpy (∆H > 0), Gibbs free energy (∆G < 0), entropy (∆S > 0), and activation energy (E_a > 0), show that the processes were endothermic, spontaneous, physical (E_a and ∆H < 40 kJ/mol), and entropy-driven. Alkalination was beneficial since the geopolymers had a higher adsorption capacity (∼8–10 times) and affinity for endosulfan (∼30 times) than the precursor material (MWFA). The adsorption mechanism entailed electrostatic interactions and hydrogen bonding. The MWFA-based geopolymers are, therefore, potential alternative low-cost adsorbents for the removal of endosulfan from water and a strategy for the valorization of MWFA.