This paper aims to study the possibility of providing a low-cost alternative for the adsorbents used in the fluoride adsorption from water by using eggshells. Indeed, eggshells were used as an adsorbent for fluoride adsorption from a drinking groundwater sample containing (2.14 mg/l) of fluoride. The eggshells were crushed and sieved into three particle sizes (0.2, 0.5, and 1mm) and then heated at different temperatures ranging from 100 to 250°C. XRD, FT-IR, pHpzc, and TG/DTA analysis were used for the characterization of the adsorbents.  Adsorption batch experiments were carried out to determine the adsorption capacity of eggshell powder such as, particle size, preparation temperature, contact time, and adsorbent dose. A spectrophotometer UV-VIS was used to assess fluoride removal efficiency. The eggshell powder heated at 250°C with 0.2mm of particle size was found to be the most efficient adsorbent, with a maximum fluoride removal efficiency of 51.4%, a maximum adsorption capacity of 0.052mg/g, and a residual fluoride concentration of 1.1mg/l within 150 minutes. The data of the adsorption kinetic on ES250°0.2 were successfully fitted with the pseudo-second-order model with a satisfying coefficient of determination (R2=0.993). The results of the intra-particle diffusion model showed a multi-linearity, revealing that the diffusion of fluoride into the adsorbent was by two stages with diffusion rate constants of Ki = 0.007 (mg /g/min1/2) and Ki = 0.001(mg /g/min1/2) for the first and second stage respectively. An adsorbent dose of 1.5g and 1 hour of contact time were sufficient to decrease fluoride concentration from 2.14 to 1.1mg/l.

This article presents that the coagulation-flocculation process is one of the water treatment processes that mainly removes dyes from aqua solution by using chemical and natural coagulants. This research was conducted to evaluate the use of chemical coagulants (ferric chloride (FeCl3), aluminum chloride (AlCl3) and natural coagulant (okra pods) to remove Vat Green 3 (VG 3) dye from aqua solution by the coagulation-flocculation process. Various experimental parameters were studied by jar test experiments such as pH, coagulant dosages, initial VG 3 dye concentration, mixing speed, and settling time. The results showed that the maximum removal efficiency of VG 3 dye was for FeCl3 97.261%, AlCl3 94.466% and okra pods 92.572% at optimum conditions pH 6 for FeCl3 and okra pods, pH 7 for AlCl3, coagulant dosage 400 mg/L for FeCl3 and AlCl3, 200 mg/L for okra pods dosage, concentration of dye 80 mg/L, mixing speed 150 rpm, and settling time 60 min for FeCl3 and AlCl3, 70 min for okra pods at room temperature 25 ± 2 oC. The maximum volume of sludge at optimum conditions was 33 mL/L, 20 mL/L, 3 mL/L for FeCl3, AlCl3, okra pods, respectively. The kinetics of the coagulation-flocculation process was obeying pseudo first order kinetics more than pseudo second order kinetics. These results indicated that the natural coagulant (okra pods) could be an alternative to chemical coagulants for removal of VG 3 dye from textile effluent due to its low cost, biodegradable, non-polluting and lower sludge production.

The paper investigated the adsorption of Cr(VI) on biochar in simulated wastewater by static adsorption method, Fourier Transform Infrared spectra (FTIR), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM) characterization analysis. The results show that biochar can effectively remove Cr(VI) in wastewater, and the adsorption equilibrium can be quickly reached within 100 min. The kinetic analysis shows that the quasi-second-order kinetic model can better fit the kinetic process of Cr(VI) adsorption by biochar, which shows that the main mechanism of the adsorption is the chemical bonding cooperation between Cr(VI) and the functional groups on the surface of biochar. Fit analysis of the isotherm at different temperatures shows that temperature increase promotes the adsorption of Cr(VI) on biochar, and thermodynamic analysis reveals that the adsorption of Cr(VI) on biochar is a spontaneous endothermic process. The Freundlich model effectively fits the adsorption isotherm of Cr(VI), indicating that the surface of biochar is uneven and Cr(VI) has undergone multilayer adsorption. The adsorption isotherm of Cr(VI) under the influence of HA and FA can be effectively fitted by the Freundlich model, and the adsorption efficiency is the highest when FA is added. The national analysis of Fourier Transform Infrared spectra (FTIR), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM) further reveals the bond cooperation between Cr(VI) and the surface functional groups of biochar. The results show that biochar has potential application value in treating chrome-containing wastewater.