Chemical Engineering Journal 81 (2001) 187–195 Sorption on natural solids for arsenic removal M.P. Elizalde-González a,∗ , J. Mattusch b , W.-D. Einicke c , R. Wennrich b a Centro de Qu´ ımica, Universidad Autónoma de Puebla, Apdo. Postal J-55, Puebla, Pue. 72570, Mexico b Department of Analytical Chemistry, Centre for Environmental Research, Permoserstr. 15, D-04318 Leipzig, Germany c Institute of Technical Chemistry, University of Leipzig, Linné-Str. 3-4, D-04103 Leipzig, Germany Received 10 September 1999; received in revised form 12 May 2000; accepted 22 May 2000 Abstract Steady state experiments were conducted on arsenic sorption from aqueous solutions by natural solids to test the feasibility of these materials to act as concentrator for arsenic removal from groundwater and drinking water. The solids considered were natural zeolites, volcanic stone, and the cactaceous powder CACMM. The arsenic species studied were As(III), As(V), dimethylarsinic acid (DMA) and phenylarsonic acid (PHA). The arsenic removed was determined from the data obtained by measuring the concentration diminution of the arsenic species in the liquid phase at equilibrium before and after the adsorption experiment by means of ICP-AES for the total concentration of arsenic and IC-ICP-MS to determine the arsenic species. The latter method allowed the detection of As(V) additionally formed as a result of the oxidation of As(III) on some of the zeolites. The sorption of the arsenic species onto zeolites was studied on both non-activated and activated zeolites, as well as on zeolites hydrogenated or modified with iron, and with respect to varying pH. The kinetics and the ability to desorb and readsorb the arsenic species were investigated for selected zeolites. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Natural solids; Arsenic; Sorption; Zeolites 1. Introduction Arsenic is ubiquitous in the environment and is a noto- riously toxic element for the general population, which is mainly exposed to arsenic via drinking water and marine food. While organic arsenic species like dimethylarsinic acid (DMA), for example, with a median lethal doses in animals LD 50 (DMA)=1200 mg kg −1 , are found as non-toxic com- pounds, the inorganic arsenite with LD 50 (As 3+ )=4.5 mg kg −1 and arsenate LD 50 (As 5+ )=14 mg kg −1 which makes no great difference, should be considered to be rather toxic. Most of the international drinking water standards are in the range of 0.04–0.05 mg l −1 arsenic which was lowered in Germany in 1996 to 0.01 mg l −1 . Consequently there is growing interest in using low-cost materials to remove arsenic from water. One promising method appears to be adsorption from solution. In the study stage this removal technique is carried out in batch experiments, columns or fixed bed reactors, and offers remarkable advantages. Triva- lent and pentavalent arsenic species in aqueous solutions were adsorbed onto activated carbon impregnated with sil- ver and copper [1], while the adsorption of organic species ∗ Corresponding author. Fax: +52-22-295-525. E-mail address: melizald@siu.buap.mx (M.P. Elizalde-Gonz´ alez). has been studied on classical carbonaceous adsorbents [2]. The adsorption of arsenic, both as As(III) and as total arsenic, has also been studied using a variety of natural materials including sand, clay, kaolinite, bentonite, mont- morillonite, goethite [3], spodic [4] and aquifer material from mining areas [5]. The removal of As(III) and As(V) has been studied in detail using antimony pentoxide and manganese dioxide [6], as well as lanthanum compounds [7], iron hydroxides [8,9] and iron-coated catalyst [10]. However, comparatively few published papers deal with ion exchange for arsenic elimination [11]. Over the last 40 years, zeolites have attracted ever- increasing interest from academic and industrial laborato- ries. They represent an important group of materials due to their catalytic, sieve and exchange properties. Natural zeolites present additionally low cost and have high oc- currence in some countries. However, metal ion exchange has chiefly been viewed as a procedure in the prepara- tion of metal zeolites for reaction promotion. Although the fast application of the cation exchange phenomenon for heavy metal removal has been described in the literature in the last few years, in the case of arsenic, where arse- nious and arsenic acid remain undissociated depending on the pH, a molecular complex sorption mechanism can be expected. 1385-8947/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S1385-8947(00)00201-1