ABSTRACT
This study reports the production of biochar adsorbents from two major crop residues (i.e., rice and wheat straw) to remove naphthenic acids from water. The alkali treatment approach was used for biochar activation that resulted in a tremendous increase in their surface area, i.e., up to 2252 and 2314 m2/g, respectively, for rice and wheat straw biochars. Benzoic acid was used as a model compound to optimize critical adsorption parameters. Its maximum monolayer adsorption capacity of 459.55 and 357.64 mg/g was achieved for activated rice and wheat straw biochars. The adsorption of benzoic acid was exothermic (∆H° = - 7.06 and - 3.89 kJ/mol) and identified possibly as physisorption (Gibbs free energy ranges 3.5-4.0 kJ/mol). The kinetic study suggested that adsorption follows pseudo-second-order kinetics with qe2 for rice straw and wheat straw-derived adsorbents at 200 and 194 mg/g, respectively. As adsorbent, the recyclability of activated biochars was noticed with no significant loss in their efficiency for up to ten successive regeneration cycles. The adsorption results were validated using a commercial naphthenic acid mixture-spiked river water and paper/pulp industrial effluent. The activated rice and wheat straw biochars exhibited excellent adsorption efficiency of 130.3 and 74.6 mg/g, respectively. The naphthenic acid adsorption on biochar surface was due to various interactions, i.e., weak van der Waal's, pore filling, π-π stacking, and ionic interactions. This study offers a cost-effective and eco-friendly approach to valorizing agricultural residues for pollutant removal from industrial wastewater, including petroleum refineries.
ABSTRACT
The current paradigm reads that calcifications characterize the advanced and complex lesions in the atherosclerotic process. To explore the possibility that coronary artery wall calcifications already commence at an early stage of atherosclerosis, a combination of proton beam techniques with a (sub-) micrometer resolution, i.e., micro-proton induced X-ray emission, backward and forward scattering spectroscopy, was applied on human coronary arteries with lesions preceding overt atheromas. The detection limits of phosphorus and calcium in each separate pixel, 0.88*0.88 microm2 in size, were approximately 150 and 80 microg/g dry weight, respectively. Calcium distributions of entire coronary artery cross section were obtained, and calcifications were demonstrated at a preatheroma stage of the atherosclerotic process. The size of the microcalcifications varied between 1 and 10 microm. The composition of the microcalcifications was deduced from the calcium-to-phosphorus ratio. In order to quantify this ratio, the thickness of the specific X-ray absorber used for PIXE had to be accurately determined. Also, thick target PIXE calculations were performed and the method was validated. The calcium-to-phosphorus ratios of the microcalcifications were assessed with good accuracy and varied from 1.62 to 2.79, which corresponds with amorphous calcium phosphate.
