Agricultural wastes as potential feedstock for activated carbons development

A. L. CUKIERMAN; P. BONELLI

Agricultural Research Updates

Nova Science Publishers

Lugar: New York; Año: 2017; p. 1 - 30

With the development ofintensive production methods for agricultural crops, considerable attention hasbeen drawn to agricultural and agro-industrial wastes management. Amongdifferent possible alternatives, this kind of wastes has been subject ofspecial interest as potential feedstock for activated carbons manufacture in thelast years. Easily available renewable sources for the sustainable productionof this widely used adsorbent have been investigated in order to fulfill thegrowing demand of activated carbons mainly associated with their increasing usein environmental pollution problems. In this framework, the present chapterexplores the feasibility of converting two abundant, underutilized agriculturalwastes into activated carbons. They include hulls from sunflower (Helianthus annuus) seeds, arising from their industrial processing for sunflower oil production, and thefield wastes remaining after harvesting sugarcane (Saccharum officinarum) stalks, generically cane trash or straw, mainly consisting of tops and leaves.The chemical activation process with phosphoric acid solution, as activatingagent, under pre-established operating conditions is applied for the conversionof both wastes. The behavior of the wastes during the thermal treatment stageof the activation process is further deepened through additional, comparativethermogravimetric measurements employing the untreated and phosphoricacid-impregnated wastes. Overall process yields of 39-42 wt% are attained. Theactivated carbons developed from the sunflower seed hulls and sugarcane strawunder the same process conditions possess porous structures characterized bytotal pore volumes of 1 cm3 g-1 and 0.75 cm3 g-1,and BET surface areas higher than 1000 m2 g-1 and of 700m2 g-1, respectively. Textural parameters for thesunflower seed hulls-based activated carbons are similar to those determinedfor a commercial sample used as a reference. These activated carbons also showa better performance in the adsorption of methylene blue, as a representative,water-contaminant basic dye, from dilute aqueous solution than the straw-basedcarbons. The samples derived from the hulls are also effective in the captureof Zn(II) ion adsorption with a maximum adsorption capacity of 4.6 mmol g-1,as judged from representing the experimental isotherms by the Langmuir model.This capacity is comparable to that evaluated for the commercial activatedcarbon. Although both wastes show potential as feedstock for their conversioninto activated carbons, the sunflower seed hulls enable to obtain adsorbents ofhigher quality than the sugarcane straw.