Abstract
A low-cost biosorbent obtained from the Palomino Fino grape seed, a Sherry wine industry by-product, has been proposed as a way of valorising this material. The biomass was characterised obtaining values of 0.68 ± 0.05 g mL−1 for bulk density, 1.02 ± 0.09 g mL−1 for apparent density and 33.3% for porosity. The pHpzc was 5.2 and the surface negative charge value was 2.4 ± 0.2 mmol g−1. The analysis of surface morphology showed differences due to the sorption. The results showed a promising potential for chromium(VI) removal from aqueous solutions. The studies were carried out in batch scale and a 23 factorial design was applied for the optimisation of the process. A percentage of 91.7 ± 0.6% was achieved for the biosorption of Cr(VI) under optimal conditions using pH 5.5, 15 g/L of biosorbent and 8 h of contact time. The biosorption capacity showed a remarkable linearity from 0 to 2 mmol L−1 Cr(VI) and a precision of 0.64% for the removal of 1 mmol L−1 of metal. Langmuir, Freundlich and Temkin isotherm equations and the parameters of six kinetic models were used in the equilibrium modelling and identifying the mechanism of the biosorption. The combination of physical and chemical sorption mechanisms was proposed for the chromium removal with a high maximum sorption capacity (qmax = 208.3 mg g−1). Thermodynamic parameters indicated the spontaneous and endothermic nature of the chromium removal. The successful biosorption was based on the special grape seed components with a relevant content in antioxidant and lignocellulosic compounds.
Highlights
Water pollution is a serious global problem which can lead to serious consequences for both the environment and human health
The bulk density (BD) is based on the space occupied by an amount of biomass particles and defined as the ratio of the mass of a powder sample and its volume, including the contribution of the inter-particulate void volume; for that, it depends on the way to pack the biomass
The values obtained for the Palomino Fino grape seed biomass were 0.68 ± 0.05 g mL−1 for BD and 1.02 ± 0.09 g mL−1 for AD, with a 33.3% of porosity and a specific surface area of 15.2 ± 0.7 m2 g−1
Summary
Water pollution is a serious global problem which can lead to serious consequences for both the environment and human health. Sugarcane or sorghum bagasse, sugar beet pulp, waste pomace of olive oil factory waste, rice and wheat straw, fruit and vegetable peels, grape wastes and other types of biomass have been utilised as low-cost sorbents for the removal of heavy metals from wastewater [11, 14] These materials are readily available in large quantities, and limited technology and expertise are required to integrate these materials into a water treatment process. Cr(0) is mainly in its metallic form as a component of iron-based alloys (such as stainless steel); Cr(III) is naturally present in rocks and soils and can be assimilated by plants; and Cr(VI) stems largely from industrial processes, is highly soluble in water and remains stable under oxidising conditions with significant mobility through soils and aquifers This element occurs in many industrial effluents from leather, textile, tanning, glass and electroplating industries as Cr(III) and Cr(VI) available. The biomass obtained from Palomino Fino grape seeds was selected in this paper to valorise this residue (produced in large amounts and available at no additional cost) for the removal of Cr(VI) from water sources
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