Agricultural Wastes as Potential Feedstock for Activated Carbons Development

A.L. CUKIERMAN; P. R. BONELLI

Agricultural Research Updates

Nova Science Publishers

Lugar: New York; Año: 2017; p. 1 - 30

With the development of intensive production methods for agricultural crops, considerable attention has been drawn to agricultural and agro-industrial wastes management. Among different possible alternatives,this kind of waste has been subject of special interest as potential feedstockfor activated carbons manufacture in the last years. Easily available renewable sources for the sustainable production of this widely used adsorbent have beeninvestigated in order to fulfill the growing demand of activated carbons mainly associated with their increasing use in environmental pollution problems. In this framework, the present chapter explores the feasibility of converting two abundant, underutilized agricultural wastes into activated carbons. They include hulls from sunflower seeds, arising from their industrial processing for oil production, and the field wastes remaining after harvesting sugarcane, generically canetrash or straw, mainly consisting of tops and leaves. The chemical activation process with phosphoric acid solution, as activating agent, under pre-established operating conditions is applied for the conversion of both wastes. The behavior of the wastes during the thermal treatment stage of the activation process is further deepened through additional, comparative thermogravimetric measurements employing the untreated and phosphoric acid-impregnated wastes. Overall process yields of 39-42 wt% are attained. The activated carbons developed from the sunflower seed hulls and sugarcane straw under the same process conditions possess porous structures characterized by total pore volumes of 1 cm3/g and 0.75 cm3/g,and BET surface areas higher than 1000 m2/g and of 700 m2/g, respectively. Textural parameters for the sunflower seed hulls-based activated carbons are similar to those determined for a commercial sample used as a reference. These activated carbons also show a better performance in the adsorption of methylene blue, as a representative, water-contaminant basic dye, from dilute aqueous solution than the straw-based carbons. The samples derived from the hulls are also effective in the capture of 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 activated carbon. Although both wastes show potential as feedstock for their conversion into activated carbons, the sunflower seed hulls enable to obtain adsorbents of higher quality than the sugarcane straw.