Biosorption of arsenic(V) with Lessonia nigrescens Henrik K. Hansen a, * , Alexandra Ribeiro b , Eduardo Mateus b a Departamento de Procesos Quı ´micos, Biotecnolo ´ gicos y Ambientales, Universidad Te ´ cnica Federico Santa Marı ´a, Av. Espan ˜a 1680, Valparaı ´so, Chile b Departamento de Cie ˆncias e Engenharia do Ambiente, Faculdade de Cie ˆncias e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal Received 25 July 2005; accepted 27 August 2005 Available online 19 October 2005 Abstract Conventional treatment methods for arsenic removal from copper smelting wastewaters create sludge that is difficult to handle. Bio- sorption of arsenic using algae as sorbent is an interesting alternative to the conventional methods. This work shows results from biosorption of arsenic(V) by Lessonia nigrescens at pH = 2.5, 4.5 and 6.5. The adsorption of arsenic could be explained satisfactorily both by the Freundlich and the Langmuir isotherms. Maximum adsorption capacities were estimated to 45.2 mg/g (pH = 2.5), 33.3 mg/g (pH = 4.5), and 28.2 mg/g (pH = 6.5) indicating better adsorption at the lower pH. These values are high in comparison with other arsenic adsorbents reported. The sorption kinetics of arsenic by L. nigrescens could be modelled well by LagergrenÕs first-order rate equation. The kinetics were observed to be independent of pH during the first 120 min of adsorption with the Lagergren first-order rate constant of around 1.07 · 10 3 min 1 . Ó 2005 Published by Elsevier Ltd. Keywords: Waste processing; Environmental; Reclamation 1. Introduction Copper smelting generates large amount of wastewater containing considerable amounts of inorganic compounds such as heavy metals and arsenic species. These wastewa- ters origin from sulphuric acid plants, which treat the SO 2 containing gases from the smelter. In order to main- tain a high quality of fresh water resources, these effluents have to be treated before the water can be returned to the ecosystems. Existing treatment methods such as sulphide or hydroxide precipitation create sludge that is difficult to handle. Furthermore, these methods consume considerable amounts of reagents in order to precipitate, coagulate and flocculate the contaminants (Gulledge and OÕConnor, 1973; Lee and Rosehart, 1972). During the last decades, the use of biosorbents has be- come interesting due to high adsorption capacities, low costs and regenerability of the sorbent (Gavrilescu, 2004; Volesky, 1990). Algae have been used for pharmaceutical reasons for detoxification of heavy metals in the human body due to a very efficient adsorption of the contami- nants, and this effect could be used to remove heavy metals from industrial wastewaters. Different algae have been ap- plied to wastewater treatment during the last decade (Davis et al., 2003; Tien, 2002; Jalali et al., 2002). One of the interesting algae that could be used to remove heavy metals from these contaminated waters is the Lessonia nigrescens, which is abundant all along the coast of Chile. The objective with this work is to test the sorption capacities and kinetics of arsenic(V) of air-dried and size reduced algae L. nigrescens. It will be analysed if the bio- sorption of arsenic follows the first-order Lagergren model, which often can be used to simplify the sorption kinetics. Finally, it will be evaluated if either the Freundlich or 0892-6875/$ - see front matter Ó 2005 Published by Elsevier Ltd. doi:10.1016/j.mineng.2005.08.018 * Corresponding author. Fax: +56 32 654478. E-mail address: henrik.hansen@usm.cl (H.K. Hansen). This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 19 (2006) 486–490