The Fankou PblZn tailings pond was abandoned in 1978, resulting in a 20 ha tailings pile requiring stabili-zation. The major constraints in rehabilitation are heavy metal (Pb, Zn, Cu and Cd) toxicity and poor nutrient conditions. A greenhouse study was conducted to evaluate the ameliorating role of river sediment, domestic refuse and inorganic fertilizers in the revege-tation of the tailings. River sediment and refuse were mixed with tailings at rates of 3070, 60% and 90% (w/w) respectively, and NPK fertilizer was also applied at four levels. Their effects on the growth of Stylo-santhes guianensis cv Graham were evaluated. River sediment and refuse amendments significantly increased dv matter yields but inorganic fertilizer had no effect. Tailings amended with 90% refuse, 30% and 60% river sediment produced higher yields. In general, plants grown on tailings amended with 30% river sediment accumulated the greatest amounts of Pb, Zn, Cu and Cd. 0 1998 Published by Elsevier Science Ltd. All rights reserved

The Lechang lead/zinc mine is located in the north part of Guangdong Province, southern China. The tailings residue from the extraction of lead/zinc ores was permanently stored in tailings ponds, which required revegetation to reduce the environmental impact. A field study was, therefore, conducted to evaluate the effects of different ameliorants, including: (1) pig manure (PM); (2) mushroom compost (MC); (3) burnt coal residue (BC); (4) fly ash (FA); and (5) surface soil on the growth of Agropyron elongatum (tall wheat grass), Cynodon dactylon (Bermuda grass), Lolium multiflorum (Italian ryegrass), and Trifolium repens (clover) in the tailings residue. The results from the core profiles indicated that adding FA (10cm) or BC (15cm) as a barrier layer between the coversoil and the tailings could increase pH, compared to the treatment with soil only. C. dactylon grew well and had a high cover (90-100%) in all the treatment plots except the control plots without any amendment. A. elongatum and L. multiflorum had a higher cover when grown in plots covered with a barrier layer using FA or BC (both with surface soil), than those grown in plots covered with surface soil only. Treatment plots receiving a thicker soil cover (30cm) had a better dry weight yield than those with a thinner soil cover (15cm), regardless of the barrier layer. The results from this study indicate that the use of either 15 cm BC or 10 cm FA as a barrier layer with surface soil, or the use of 38 tonnes PM/ha and 6 cm MC, were effective for the revegetation of Pb/Zn mine tailings. C. dactylon was the best species among the four species used for revegetation.

The acid-forming potential of lead/zinc (Pb/Zn) mine tailings at Lechang City of Guangdong Province was studied using both net acid generation (NAG) and acid

The goal of the present study was to assess a soil seedbank as an input seed source for revegetating lead/ zinc (Pb/Zn) mine tailings. The seed bank source was abandoned farmland, whose top 10-cm layer of topsoil contained 6,850 377 seeds/m 2 from 41 species. The seeds in the soil were principally distributed in the upper 0-2 cm, which held 75.8% of total seeds and 92.7% of species composition. The top 2-cm layer oftopsoil may be sufficient to serve the purpose of providing a seed source for revegetation on derelict lands, including mined lands. Four different thicknesses of topsoil (1, 2, 4, and 8 cm, redistributed from the total 0-10-cm layer from the farmland) were field-tested on the Pb/Zn mine tailings. There was no significant difference in seedling density among the 4 thickness treatments. Many seeds in the treatments with more than 1-cm of topsoil were unable to emerge from the deeper layer. Seedlings in plots with topsoil of 1-, 2-and 4-cm failed to establish within lyear due to the extremely high acidity (pH 2.39 to 2.76). A shallow layer of topsoil cannot neutralize the sulfuric acid generated from oxidation of pyrites in the tailings. For establishment of seedlings on metalliferous lands, an insulating layer such as subsoil, building rubble, or domestic refuse is necessary before covering with valuable top-soil. The woody legume Leucaena leucocephala grown on the tailings with a topsoil cover of 8-cm was the most dominant species. Lead was accumulated in root, branch, stem bark, and xylem, which accounted for more than 80% of the total metal concentration in the plant. This portion of Pb will reside in the plant for a long period, while the smaller portion of Pb in the leaf (about 15%) could be returned to the environment as litter during growth. Woody plants may have an advantage in metalphyto-remediation over herbaceous plants.

The residues from the extraction of lead/zinc (Pb/Zn) ores of most Pb/Zn mines are permanently stored in tailings ponds, which require revegetation to reduce their environmental impact. This can only be done if the main constraints on plant establishment are evaluated. This can readily be done by field and greenhouse studies. To test this, the properties of different tailings from Lechang Pb/Zn mine located at the north of Guangdong Province in southern China have been studied. Physical and chemical properties including concentrations of metals (Pb, Zn, Cd and Cu) in the tailings and soils collected from different sites have been measured. The results showed that tailings contain low nitrogen (0.016-0.075%), low-organic matter (0.58-1.78%), high salt (3.55-13.85 dS/m), and high total and diethylene-tetramine-pentaacetic acid (DTPA)-extractable metal concentrations (total: 1019-1642 lgg 1 Pb, 3078-6773 lg glZn, 8-23 lgg 1 Cd, and 85-192 lg g 1 Cu; DTPA-extractable: 59-178 lgg 1 Pb, 21-200 lgg 1 Zn, 0.30-1.5 lg gl Cd, and 4.3-12 lg gl Cu). Aqueous extracts of tailings/soils (10%, 20% and 30%, w/v) from different sites were prepared for testing theire ects on seed germination and root elongation of a vegetable crop Brassica chinensis and a grass species Cynodon dactylon. It was found that root elongation provided a better evaluation of toxicity than seed germination. The ranking of toxicity using root elongation was: high-sulfur tailings>tailing dam>sparsely vegetated tailings> densely vegetated tailings>mountain soil for both plants. This order was consistent with DTPA-extractable Pb contents in the tailings and soils. B. chinensis seedlings were then grown in the mixtures of different proportions of tailings and farm soil for-weeks, and the results (dry weights of seedlings) were in line with the root elongation test. All these demonstrated that heavy metal toxicity, especially available Pb, low content of nutrient, and poor physical structure were major constraints on plant establishment and colonization on the Pb/Zn mine tailings. 2002 Published by Elsevier Science Ltd.