article · Particulate Science And Technology
Powdered walnut shell treated with orthophosphoric acid produces an effective activated carbon adsorbent for removing Congo red dye from aqueous solutions. In batch-adsorption tests, dye uptake increased with longer contact times and higher initial dye concentrations. The highest removal rate reached 94.53 percent at an optimum pH of 3.12. Equilibrium data aligned closely with the Langmuir isotherm model, showing a maximum monolayer adsorption capacity of 40 milligrams per gram, while kinetic data followed a pseudo-second-order model. Thermodynamic calculations confirmed that the adsorption process is spontaneous and endothermic. Furthermore, the carbonised material was successfully regenerated using a dilute hydrochloric acid solution. Across three consecutive regeneration cycles, the adsorbent maintained a Congo red removal capacity between 90 percent and 93 percent, demonstrating its potential for reusable wastewater treatment.
Synthetic dyes in industrial effluent pose environmental risks and are often difficult to treat cost-effectively. Utilising agricultural by-products such as walnut shells to create activated carbon offers an accessible method for capturing hazardous dyes from water. Demonstrating high removal efficiency and simple chemical regeneration over multiple cycles shows that low-cost waste materials can help address industrial water pollution challenges.
This study provides early-stage laboratory evidence for using functionalised walnut shell waste as an adsorbent for industrial dye removal. It could enable water treatment facilities and textile manufacturers to lower effluent treatment costs using agricultural waste. The technology remains at a batch laboratory stage, requiring pilot testing, continuous-flow evaluation, and life-cycle economic assessments before it can be considered for real-world or commercial deployment.
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This study investigates the adsorption of Congo red dye on walnut shell powder based activated carbon in batch process (WNAA). Walnut shell powder was carbonized by treating with phosphoric acid (H3PO4), and the adsorbent was characterized using Fourier Transform-Infrared spectrophotometer (FT-IR), Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDX), and pH point of zero charge (pHpzc), respectively. Operational parameters such as contact time, initial dye concentration, and pH were investigated using batch-adsorption techniques. The adsorption uptake was found to increase with increase in initial dye concentration and contact time. The optimum CR dye uptake was observed at pH 3.12 corresponding to 94.53% removal. Pseudo-first-order, pseudo-second-order, Elovich, and Intraparticle diffusion kinetic models were used to test the adsorption data. The pseudo-second order exhibited the best fit out of the four kinetic models used. Equilibrium data were fitted to the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. Langmuir model fitted the adsorption data most with maximum monolayer coverage of 40 mg/g. Thermodynamic parameters such as Gibbs free energy, enthalpy, entropy, and the activation energy were determined. It was found that Congo red dye adsorption was spontaneous and endothermic. 0.02M Hydrochloric acid was used to regenerate the adsorbent prepared, and the regenerated adsorbent was used for dye adsorption. Congo red dye adsorption capacity ranged from 90% to 93% at three consecutive times. This study has shown that walnut shell is a good adsorbent in the treatment of Congo red dye from aqueous solutions.
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DOI: 10.1080/02726351.2017.1340914
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