Mining,beneficiation,smelting,and other copper(Cu)-industry activities eventually produce undesired waste materials,including tailings,slags,anode sludge,and others that are dumped in open fields.The abandoned Cu waste materials stacked in the open field may compound the problem of heavy metal leaching,contaminating the surrounding soil and groundwater.Therefore,the study on the release characteristics of heavy metals will offer a convenient approach to evaluating management methods and disposal techniques to prevent heavy metal contamination,which is of great significance for the pollution control and risk reduction of heavy metals in Cu waste materials.This research was conducted using different Cu waste materials,including Cu tailings,water-quenching slag,Cu ore,smelting dust,anode sludge from a deserted copper mining and smelting industry located in Bofang County,Hunan Province.The Physicochemical and environmental availability of Cu waste materials and leaching test with Toxicity characteristic leaching procedure(TCLP),Synthetic precipitation leaching procedure(SPLP)and the batch experiment under various conditions,including p H of acid rain,temperature,and liquid to solid(L/S)ratio,and a batch leaching test with artificial root exudates of organic acids were conducted to analyze the release characteristics of heavy metals leaching,their chemical speciation changes,and mineral phase transformation.The results are as follows:(1)The elelment analysis results show that the total contents of As,Cd,Cu,Pb,Zn and other heavy metals in the waste residue are very high,and the proportion of active fraction of each heavy metal according to BCR sequential extraction metod was also high.The metal with high proportion of acid soluble state and reducible state was followed as Cd>Zn>Cu>Pb.Though As was mainly existed in residue fraction,the proportion of total active chemical forms was high.The concentrations of some heavy metals in the TCLP and SPLP leachates from soot,anode sludge and tailings exceed the corresponding element threshold values of the TCLP and toxic leaching standards(GB 5085.3-2007),and these slags can be classified as hazardous wastes with moderate to high risks to the environment.(2)The batch leaching test under various environmental factors,including different p H of acid rain(3.0,4.5,5.6,7.0),temperature(15,25,35,45 oC),and L/S ratio(5:1,10:1,20:1,30:1)conducted on the release of As,Cd,Cu,Pb,and Zn,revealed that the waste residue had a potential buffering capacity for the acidic solution.Leachate p H stabilized in the range of 7.21-7.63.The low p H(4.5)and high temperature(35-45oC)could significantly promote heavy metal release.The L/S ratio above 20:1 significantly decreased heavy metal leachate concentrations,with 5:1 resulting in higher concentrations of As and heavy metals.The leachate concentrations of metals were high at the early stage leaching of 24 h and then slightly reduced as the time progressed.The concentrations of As,Cd,Cu,Pb,and Zn from the leaching solutions ranged from 0.81-3.05,0.011-0.094,0.74-3.09,0.58-2.98,and 1.45-13.75 mg/L,respectively.The high leachability of the element in leachate was observed for As>Cu>Cd>Zn>Pb with 3.48%,1.01%,1.03%,0.41%,and 0.80%,respectively,which was also associated with their predominated potential active fractions and mineral phases.Based on modeling calculations,the key solubility-controlling phases of As were partly controlled by newly formed Cd,Zn,Cu,and Pb arsenates;Cd,Cu,Pb,and Zn were determined by their various hydroxides(OH-),oxides(O(2)),and sulphates(SO42-)bearing minerals following dissolution/precipitation mechanisms.The SEM analysis also revealed that the surface of the original slag after leaching was reduced and loosened.The XRD analysis for leached water quenched slag showed that peak intensities of the minerals phases,including fayalite,quartz,and other minor minerals,weakened after leaching at p H 4.5 due to the H+attack,which damaged the chemical bonds resulting in the dissolution of As,Cd,Cu,Pb,and Zn in leachate.The XPS spectra results revealed that As 3d,Cd 3d,Cu 2p,Pb 4f,and Zn 2p in slag existed as As O43-,Cd SO4,Cu+,Pb SO4,and Zn Si O3,after leaching respectively,indicating the dissolution of metals in leachate.(3)The leaching test under various simulated root exudates of organic acids of citric acid,oxalic acid,lactic acid and acetic acid with different levels of 1 m M,5m M,and 10 m M was conducted to investigate the influence of root exudates on heavy metals(Cd,Cu,Pb,and Zn)released from the water quenching slag.Higher acid concentrations(5 and 10 m M)had a faster rate of mobilization and dissolution of all heavy metals tested than lower acid concentrations(1 m M).Under 10 m M organic acid leaching,the concentration ranges of Cd,Cu,Pb and Zn was 0.49~3.32,9.50~47.32,2.30~37.5,12.3~88.2 mg/L,respectively.Moreover,different acids had different dissolution rates following the order of citric acid>oxalic acid>lactic acid>acetic acid.Moreover,the bioavailability and mobility among the four heavy metals(Cd,Cu,Pb,and Zn)from the water quench slag were highly observed for Zn>Cu≈Pb>Cd.The XPS spectra for C 1s with the different treatments revealed that the proportion of COO-fitting peak areas increased markedly after leaching with the organic acids.To sum up,these results suggest that As,Cu,Pb,and Zn in the Cu waste materials could pose a severe threat to the surrounding environment;therefore,developing appropriate disposal techniques for the waste residues is necessary to prevent heavy metal pollution.20 Figures,10 Tables,267 References... |