Pergamon Applied Geochemisrry, Vol. 11, pp. 343-346, 1996 Copyright 0 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0883-2927/96$15.00+0.00 0883-2927(9!5)00043-7 The suitability of brown coal as a sorbent for heavy metals in polluted soils Anna Karczewska, Tadeusz Chodak and Jaroslaw Kaszubkiewicz Institute of Soil Science and Agricultural Environment Protection, Agricultural University of Wrodaw, ul.Grunlwaldzka 53, 50-357 Wrodaw, Poland Abstract-The aim of the study was to evaluate the suitability of brown coal from the strip surface mine “Sieniawa” for the reclamation of soils polluted with Pb and Cu and still exposed to metal emissions. A column experiment was carried out in order to estimate the sorption capacity of brown coal with respect to Pb and Cu as well as to examine its protective effects if mixed with limestone and used on the surface of polluted,sandy soil. Columns filled with soil and covered with a layer of coal + limestone were percolated with solutions of Pb and Cu nitrates. The metal load added to the soil considerably exceeded the soil and coal CEC. Finally, some of the columns were percolated with NHdOAc in order to release the adsorbed metals. It was shown that brown coal mixed with ground limestone was efficient in immobilizing Pb and Cu. Not only adsorption but also complexation and precipitation were involved in the immobilization process. A homogeneous layer of brown coal and limestone covering the soil surface gave better protective results than if mixed with the soil. Copyright 0 1996 Elsevier Science Ltd INTRODUCTION (I) brown coal alone; Numerous experiments carried out for many years have proved the suitability of brown coal (lignite) for the improvement of physical and chemical properties of light soils and for increasing crop production (BereSniewicz and Nowosielski, 1976; Augustyn, 1991). In recent years, much research work has focused on using the brown coal for soil remediation and reclamation, in particular in the areas polluted by the emissions from metal smelters (Szerszeri et al., 1993). One of the most promising methods of heavy metal immobilization in light soils strongly polluted with metallurgical dust consists of covering the soil with a layer of brown coal mixed with ground limestone. Such a measure should cause an effective metal immobiliza- tion due to the big specific surface and high content of humic compounds in brown coal, its high CEC values (Augustyn et al., 1989) as well as a protective action of limestone against the pH value decrease. The main aim of the research presented in this paper was to examine sorptive properties of brown coal from the “Sieniawa” surface mine (situated in the SW part of Poland) and to estimate the suitability of this coal for reclamation of soils strongly polluted with heavy metals, in particular with Cu and Pb. MATERIAL AND METHODS Polyethylene columns of about 1.6 dm’ volume were filled with brown coal, quartz sand and with polluted soil in 6 different variants: (II) quartz sand covered with a 4 cm layer of mixed brown coal + 20% ground limestone; (III) same as II but the covering layer was mixed with soil to the depth of 15 cm; (IV) uncovered (unprotected) polluted soil; (V) polluted soil covered with a 4 cm layer of mixed brown coal + 20% ground limestone; (VI) same as V but the covering layer was mixed with soil to the depth of 15 cm. Both brown coal and ground limestone were sieved through the 2-mm screen prior to the experiment. The specific surface of brown coal determined by sample saturation with glycerine vapour, was 180 m*/g. The polluted soil used in the experiment originated from the vicinity of the copper smelter “GIogbw”. Some characteristics of the soil are-shown in Table i. CEC and exchangeable bases were determined in 1 M NHdOAc (pH 7.0). Total concentrations of heavy metals in the soil were measured by flame AAS after digestion with aqua regia. The columns were percolated with solutions containing mixed nitrates of Cu and Pb (50% + 50%) under unsaturated conditions, so that the redox conditions remained oxidizing throughout the duration of the experi- ment. The daily rate of solution was 100 cm3 (i.e. 9.0% of total pore volume) at the beginning of the experiment (first 25 days), 250 cm3 (22.5% of pore volume) in the second phase (22 days), 500 cm3 (45% of pore volume) in the third phase (6 days) and again 250 cm3 (of more concentrated solution) during the last 8 days. The metals concentration in the solution was 1000 mg/dm3 in the first 53 days and 5000 mg/ dm” in the last 8 days. The total metals load applied to each column during the 3 months was 21.1 g (see Fig. 1). Then, selected columns (variants: I, III, IV and VI) were percolated with 0.1 M NHaOAc (PH 7.0) in order to release the adsorbed metals. The percolates (effluents) were collected and analysed for Cu and Pb concentrations using flame AAS. The experiment was performed in 3 replications and all data reported in the paper represent the mean values. 343