We aimed to obtain magnesium/iron (Mg/fe)-layered double hydroxides (LDHs) nanoparticlesimmobilized on waste foundry sand-a byproduct of the metal casting industry. XRD and ft-iR tests were applied to characterize the prepared sorbent. The results revealed that a new peak reflected LDHs nanoparticles. In addition, SEM-EDS mapping confirmed that the coating process was appropriate. Sorption tests for the interaction of this sorbent with an aqueous solution contaminated with congo red dye revealed the efficacy of this material where the maximum adsorption capacity reached approximately 9127.08 mg/g. The pseudo-first-order and pseudo-second-order kinetic models helped to describe the sorption measurements, indicating that the physical and chemical forces governed the removal process. The severity of water pollution has been resulted from the economic development adopted by human overall the world. The different industries such as textile, plastic, coating, and paper utilize the "dyes" in the different manufacturing stages 1-3 These compounds, even at extremely low concentrations can cause a significant contamination and, consequently, the destroying of the ecosystem elements 4-6. The continuous discharge of water contaminated with poisonous dyes to the environment can be formed a potential threat to the aquatic life and human health especially that the dyes are intrinsically toxic 7,8. Therefore, economical and highly efficient techniques need to be developed for treatment of the contaminated water 9-11. The presently available techniques include photocatalysis 12 , biodegradation 13 , chemical coagulation 14 , ion exchange 15-17 , and adsorption 18-22. The adsorption is one of the most valuable methods in the treatment of the aqueous solutions because of its high efficiency, ease of operation, low cost of operation, and easy desorption 23-25. The selection or fabrication of the adsorbents is the main operative point of adsorption, where these materials must be highly stable, low cost, environment-friendly, and definitely efficient 26,27. Until date, literatures have been reported different reactive materials containing activated carbon, zeolite, clay, chitosan, montmorillonite, and vermiculite 7. However, several disadvantages of these materials include the high cost, poor adsorption capacity, and low reuse rate, which limits their usage 28,29. Thus, finding more efficient, longer durability and low cost new adsorbents are a difficult but a vital task. Layered double hydroxide (LDH) is a type of layered anionic compound that is joined via a non-covalent bond-an interaction between non-framework interlayer anions and positively charged main lamellar. Its general formula is [M +2 1-x M +3 × (OH) 2 ] x + [An − x/n •mH 2 O] x − , where, M +3 is a trivalent metal ion such as Fe +3 , Cr +3 , Sc +3 , and Al +3 ; M +2 is divalent metal ions such as Mn +2 , Mg +2 , Ni +2 , and Zn +2 ; An − is an anion that balances the interlayer charge such as Cl − , OH − , NO 3 − , and CO 3 −2 ; x is the ratio of M +3 / (M +3 + M +2), var...

Reaction term in the transport equation which described the migration of metal ions in the porous medium is frequently represented by conventional kinetic models such as pseudo-first order, pseudo-second order, and others. Unfortunately, these models are applicable for the constant value of solution pH, and they cannot simulate the real situation in the field scale where this pH may be changed with time. Accordingly, the present study is a good attempt to derive the kinetic model that can simulate the change in the pH of the solution through solute transport. This was achieved by modifying the adsorption capacity and reaction constant to be functions in terms of solution pH by using semianalytical analysis and numerical approximation. The results proved that the kinetic model based on the numerical approximation (using exponential functions for adsorption capacity and reaction constant) symbolled as model 2 was more representative from other models applied for the description of interaction of nickel ions (with initial concentration of 400 mg/L) and cement kiln dust with sum of squared error ≤1.54913 and determination coefficient ≥0.889. Also, the developed models had high ability for recognizing between pure precipitation and pure adsorption.

In batch mode, the adsorption characteristics of S 2¯i ons on Lagenaria siceraria mesocarp, pedicle and peel as raw materials have been studied in comparison to remove sulfide ions from tanneries waste water, under various parameters such as adsorbent dosage, contact time, agitation speed and pH. Maximum removal efficiency (70.96%) was observed on L. Siceraria peel followed by pedicle (51.58%) and mesocarp (29.57%) for adsorbent dosage of 0.10 g/L peel for 50 ml solution of sulfide (20 mg/L). The adsorption process was rapid, and it reached equilibrium in early 20-35 min for all adsorbents. Freundlich and Langmuir adsorption isotherms were employed for mathematical description of the adsorption equilibrium and to explain mechanism of adsorption.The maximum amounts of sulfide ions adsorbed, as evaluated by Langmuir isotherm, was 1.0436 mg/g of LS pedicle, 0.886 mg/g of peel and 0.843 mg/g of pedicle. The adsorption process conforms well to a pseudo second order kinetic model with best adsorption results at pH 8.

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