The adsorption of cadmium from simulated mining wastewater by coal waste (CW) and calcination-Modified coal waste (MCW) was investigated. Effects of pH, initial concentration, particle size of adsorbent, adsorbent dosage and temperature were studied in batch experiments. The adsorption efficiency for cadmium increased with increasing pH, and the optimum pH for cadmium adsorption onto MCW and CW was 6.0 and 6.5, respectively. Kinetic experiments showed that the adsorption equilibrium was reached within 120 min and followed pseudo-second-order model well. The adsorption isotherm data fit Langmuir and Freundlich models, and the adsorption capacity of cadmium on the two adsorbents increased with increasing temperature from 298 to 318 K. MCW had a higher adsorption capacity of cadmium than CW, because calcination treatment can make CW to have more loose structure and higher specific surface area. Thermodynamic parameters, the Gibbs free energy change (DG0), enthalpy change (DH0) and entropy change (DS0), were calculated and the results showed that the adsorption of cadmium on CW and MCW was spontaneous and endothermic. Fourier transform infrared studies indicated silanol and aluminol groups were responsible for cadmium binding. The desorption results indicated that the two adsorbents could be used repeatedly at least three times without significant decrease in the adsorption capacity for cadmium. The results suggested that Modified CW could have high potential as low-cost adsorbent for cadmium removal.

In the present study, an organic wastewater industrial pollutant such as a phenol was removed by the improved Modified adsorbents: NH3-activated carbon, and NaOH-activated. When the activated carbon ACDK was recovered from agricultural waste Date Kernel and prepared via pyrolysis and thermal activation at 850 ° C. The modification of the activated carbon surface ACDK was ready chemically with the impregnation in the 10wt %   ammonia solution to obtain a Modified adsorbent: NH3-ACDK, the impregnation of ACDK in 10 wt% Sodium Hydroxide solution for the second Modified adsorbent: NaOH-ACDK. The Modified functional samples were characterized by SEM, FT-IR and DRX, TGA-DSC. The results established that phenol molecules were favorable for adsorption on the nitrogen group and hydroxide group of activated carbon at pH 4, solution temperature (28°C), and contact time (60-100 minutes). The adsorption kinetics of phenol on the Modified adsorbents were better adapted to the pseudo-second-order adsorption model with (R² = 0.985) for NH3-ACDK, (R² = 0.980) for NaOH-ACDK. The adsorption isotherm follows the Langmuir design and is fitted well compared to Freundlich models with (R2= 0,999) for NaOH-ACDK, Langmuir, and Freundlich isotherms models fit the experimental equilibrium data for NH3-ACDK) with correlation coefficient (R²≥ 0,989). The removal percentage of phenol on NH3-ACDK, and NaOH-ACDK was 97,6 % and 70,3%, respectively.

In this work, adsorbents, namely bentonite and sludge, Modified by iron and copper were used to remove the H2S and mercaptan from Kermanshah refinery. The used adsorbents are inexpensive materials, which substantially decrease the operational costs. The structure of the adsorbents was analyzed using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). The effects of gas and flow rate on the H2S and mercaptan removal were also studied. The results indicated that the bentonite Modified by iron has a high capacity for removing H2S (32. 256 mg/g) and mercaptan (0. 98 mg/g). Moreover, the adsorption capacity of the sludge Modified by copper for removing H2S and mercaptan was 11. 18 and 0. 81 mg/g respectively. Furthermore, by increasing the flow rate and concentration of H2S and mercaptan, H2S and mercaptan concentrations in the sludge output gas increased, but no considerable change was observed in the bentonite output gas.

Adsorption may be used to process significant metal particles in contaminated wastewater by various methods. The authors looked at various adsorbents for the expulsion of Ni(II) particles from an aquatic environment by different researchers. This paper aims to gather scattered open knowledge on a large variety of potentially persuasive adsorbents for the removal of Ni(II) particles. The present work on the usage of nickel by various natural/Modified adsorbents was studied profoundly, for example, natural/Modified agricultural waste, agricultural activated carbon, algae, fungal and, aquatic plant biomasses. This performance was assessed for removal efficiency and the sorbent capacity of used natural/waste materials in the system processes. Isotherm and kinetic study results were obtained from pH solution equilibrium contact time, adsorbent dose, initial metal concentration, and temperature of various adsorbents toward the Ni(II) particles to be examined. A documented analysis of reputed published papers revealed that industrial solid waste products, natural materials, and biosorbents have extraordinary Ni(II) adsorption ability from wastewater.

Phosphorus (P) is considered the leading cause of eutrophication in natural waters and has received considerable attention recently from the scientific community. In this study, P removal from aqueous solutions was investigated using bentonite, kaolinite, calcite, and zeolite mineral adsorbents Modified with extract of walnut shell and wheat straw, chitosan, sodium carboxymethyl cellulose (CMC), and malic acid. Phosphorus sorption was evaluated using adsorption isotherms equations. Modified adsorbents with chitosan obtained the maximum sorption capacity of P. The results showed that P sorption capacity by Chitosan-adsorbents (bentonite (0.35 mg/g), calcite (2.09 mg/g), kaolinite (0.41 mg/g) and zeolite (0.43 mg/g)) was improved by ~ 129, 102, 128 and 119%, respectively compared to unModified adsorbents (bentonite (0.27mg/g), calcite (2.04 mg/g), kaolinite (0.32 mg/g) and zeolite (0.36 mg/g). Langmuir and Freundlich models were used to simulate the sorption of P on Modified adsorbents. The double layer model (DLM) could predict P adsorption by Modified adsorbents over a wide pH range and varying ionic strength. Thermodynamic parameters showed that the nature of P adsorption by these adsorbents was non-spontaneity nature.

Modified adsorbents have been introduced by researchers to overcome the shortcomings of conventional ones. These are including a wide range of adsorbents prepared from combination of organic, inorganic and polymeric materials. Most widely used Modified adsorbents for removal of pollutants from aqueous solutions, classified as silica and polymer-based adsorbents. The present review focuses on synthesis, applications and adsorption performance of these Modified adsorbents. In a comparative look, using functionalized silica is a simple and effective method for removal of heavy metals, while the functionalized polymeric adsorbents can be used to remove organic compounds. Also polymeric chelating adsorbents and polymeric/inorganic adsorbents mainly used for removal of heavy metals.