In the present research, zeolite is used for the removal of toxic Congo red dye from water solution. The effects of different operating conditions such as hydrogen potential (pH), contact time (time), zeolite dose (D), initial dye concentration (C₀), and ionic strength (I) are investigated for Congo red adsorption under batch mode. It was found that the adsorption process was greatly affected by the initial pH of the dye solution. The removal efficiency decreased from 97.68 to 5.22% when the pH varied from 3 to 5; thus, acidic conditions clearly improve Congo red adsorption on zeolite. At pH 3, an increase in C₀ and I and decrease in D resulted in an increase in the adsorption capacity q_e. The effects of these three parameters and their interactions were also investigated using the 2³ full factorial design experiments approach where q_e was chosen as the response. The results obtained from this method followed by the analysis of variance and the Student’s t-test show that, the influence of these parameters on dye adsorption process are in the order I < C₀ < D. The kinetic studies revealed that adsorption follows a pseudo-second-order kinetic model. The adsorption isotherms experimental data were analyzed using the Langmuir, Freundlich, and Temkin isotherms models. The Freundlich isotherm was the best-fit model to the experimental data. The fitting of kinetics and isotherm models was evaluated by using non-linear modeling, R², MSE, and RMSE.

This study investigated the potential of 4A zeolite, named4AZW in this work, generated by natural gas dehydration units as solid waste after several treatment cycles, as a low-cost adsorbent to separately remove two cationic dyes, methylene blue (MB) and malachite green (MG), from an aqueous solution within a batch process. The adsorbent material was characterized by N₂gas adsorption–desorption, X-ray fluorescence spectrometry, X-ray diffraction, FT-IR spectroscopy, and the determination of its cation exchange capacity and point of zero charge. The influence of key operating parameters, such as the pH, adsorbent dosage, ionic strength, contact time, initial dye concentration, and temperature, was investigated. Three independent variables acting on MB adsorption performance were selected from the Box–Behnken design (BBD) and for process modeling and optimization. An analysis of variance (ANOVA), an F-test, and p-values were used to analyze the main and interaction effects. The experimental data were satisfyingly fitted with quadratic regression with adjusted R²= 0.9961. The pseudo-second-order kinetic model described the adsorption of the dyes on 4AZW. The equilibrium data were well-fitted by the Langmuir model for each adsorption system (MB-4AZW and MG-4AZW) with maximum adsorption capacity (q_max) values of 9.95 and 45.64 mg/g, respectively, at 25 °C. Thermodynamics studies showed that both adsorption systems are spontaneous and endothermic.

Prior studies have examined the ability of Moringa oleifera (MO) seed extract, among other natural coagulants, to remove several types of dyes. MO has been proven to have a high capacity to remove some anionic dyes. The aim of the present study is to explore the possible use of aqueous and saline extracts of MO as biocoagulants for the removal of Mordant Black (MB11) from aqueous solution. Their performances were compared to that of aluminum sulfate (alum). To do so, various operating parameters were investigated such as coagulant dose (100–600 mg/L), pH (3–11), initial dye concentration (100–350 mg/L), sodium chloride concentration (0.2–2 M), and sedimentation time (15–90 min). The maximum percentages of MB11 removal were found to be 98.65%, 80.12%, and 95.02% for alum, aqueous extract of MO (MOPW), and saline extract of MO (MOPS), respectively, at around pH 6.5 and for coagulant doses of 400 mg/L (alum) and 500 mg/L (MOPW and MOPS). The coagulation-flocculation mechanism of biocoagulants was hypothesized to be adsorption and charge neutralization. The two biocoagulants (MOPW and MOPS) showed an interesting versatility towards pH counter to alum which was very sensitive to this parameter. pH variations were measured for the three coagulants and proven to be negligible for the biocoagulants. Faster sedimentation time was recorded when MOPW and MOPS were used, suggesting the existence of larger quickly settleable flocs. Considering their high coagulative capacity, rapid and cost-effective preparation, and eco-friendly character, MO extracts can be considered as powerful alternatives to aluminum sulfate in the remediation of MB11 from wastewaters.

This work focuses on studying the removal of Titan Yellow (TY) dye, which is a water pollutant using three matrices of layered double hydroxide (LDHs; M⁺²Al-HT), with M⁺² = Ni, Co, or NiCo were synthesized using the co-precipitation technique in a solution with a constant pH. The X-ray diffraction (XRD) pattern of the formed solids shows that the synthesized phase is the LDH type with the average interlamellar distance (d_spacing ≈ 7.595 Å). The Fourier-transform infrared spectroscopy (FT-IR) spectra were compared, before and after adsorption, confirming the displacement of the carbonated interlayers and confirmed the presence of the S=O bond in the dye under study. Thermogravimetric-differential thermal analysis (TG/DTG) shows temperatures of decarbonation of the LDHs. The BET specific surface areas of NiAl-HT, NiCoAl-HT, and CoAl-HT were found equal to 156.819 m²∙g⁻¹, 142.72 m²∙g⁻¹, and 56.98 m²∙g⁻¹, respectively, and the SEM-EDX micrographs results confirmed the creation of the hydrotalcite type material. The UV–visible study of the adsorption of TY is performed by varying different parameters such as pH of the solution, mass, contact time, and temperature. The obtained isotherms from this kinetic study show that the adsorption of TY dye is more efficient in NiAl-HT. It can, therefore, be stated that the adsorption process of TY is endothermic and spontaneous. The results of this study could be extended to other anionic azo dyes having similar chemical structures.