Degradation of digested sewage sludge residue under anaerobic conditions for mine tailings remediation

Previous studies showed that 85 % of total organic matter (TOM) in digested sewage sludge (biosolids) used as a sealing layer material over sulfide tailings at the Kristineberg Mine, northern Sweden, had been degraded 8 years after application, resulting in a TOM reduction from 78 to 14 %. To achieve a better understanding of the field observations, laboratory studies were performed to evaluate biodegradation rates of the TOM under anaerobic conditions. Results reveal that the original biosolid consisted of ca. 60 % TOM (48.0 % lignin and 11.8 % carbohydrates) that had not been fully degraded. The incubation experiments proved that 27.8 % TOM in the biosolid was further degraded anaerobically at 20–22 °C during the 230 days’ incubation period, and that a plateau to the biodegradation rate was approached. Based on model results, the degradation constant was found to be 0.0125 (day^?1). The calculated theoretical gas formation potential was ca. 50 % higher than the modeled results based on the average degradation rate. Cumulated H₂S equated to 0.65 μmoL g^?1 of biosolid at 230 days. However, the large sulfurous compounds reservoir (1.76 g SO₄ ^2? kg^?1 biosolid) together with anaerobic conditions can generate high concentrations of this gas over a long-term perspective. Due to the rate of biodegradability identified via anaerobic processes, the function of the biosolid to serve as an effective barrier to inhibit oxygen migration to underlying tailings, may decrease over time. However, a lack of readily degradable organic fractions in the biosolid and a large fraction of organic matter that was recalcitrant to degradation suggest a longer degradation duration, which would prolong the biosolid material’s function and integrity.     

The effect of sewage sludge on salt-marsh denitrifying bacteria

Sewage sludge was applied biweekly to the soil surface of a shortSpartina alterniflora marsh in order to evaluate the marsh’s ability to assimilate the sludge nitrogen. After nine months there was a significant decrease of the denitrification potential in the first 15cm of the soil profile. In laboratory experiments the sludge was shown to have an immediate inhibitory effect on potential soil denitrification rates indicating that the decreasedin situ potential was probably a result of direct toxicity of the sludge on this bacterial respiratory process.     

Using sewage sludge as a sealing layer to remediate sulphidic mine tailings: a pilot-scale experiment, northern Sweden

At the Kristineberg mine, northern Sweden, sulphidic mine tailings were remediated in an 8-year pilot-scale experiment using sewage sludge to evaluate its applicability as a sealing layer in a composite dry cover. Sediment, leachate water, and pore gas geochemistry were collected in the aim of determining if the sludge was an effective barrier material to mitigate acid rock drainage (ARD) formation. The sludge was an effective barrier to oxygen influx as it formed both a physical obstruction and functioned as an organic reactive barrier to prevent oxygen to the underlying tailings. Sulphide oxidation and consequential ARD formation did not occur. Sludge-borne trace elements accumulated in a reductive, alkaline environment in the underlying tailings, resulting in an effluent drainage geochemistry of Cd, Cu, Pb and Zn below 10 μg/L, high alkalinity (810 mg/L) and low sulphate (38 mg/L). In contrast, the uncovered reference tailings received a 0.35-m deep oxidation front and typical ARD, with dissolved concentrations of Cd, Zn and sulphate, 20.8 μg/L, 16,100 μg/L and 1,390 mg/L, respectively. Organic matter degradation in the sludge may be a limiting factor to the function of the sealing layer over time as 85 % loss of the organic fraction occurred over the 8-year experimental period due to aerobic and anaerobic degradation. Though the cover may function in the short to medium term (100 years), it is unlikely to meet the demands of a long-term remedial solution.     

Composting of olive processing wastes and tomato stalks together with sewage sludge or dairy manure

In this study, composting of olive pomace from three-phase oil production system, sewage sludge, dairy manure, and tomato stalks were carried out. The effects of carbon/nitrogen ratio on decomposition rate of composting were investigated with constant free air spaces of composting mixtures. Composting process was carried out in the aerobic reactors made of stainless steel which were monitored for 32 days. Temperature-controlled feedback system was operated based on the Rutgers strategy. Temperature, moisture, organic matter, pH, electrical conductivity total carbon, total nitrogen, ammonium nitrogen and nitrate nitrogen, total phosphorus as well as potassium were monitored during the composting process. In addition, mass and volume changes of the mixtures were determined. The highest degree of decomposition was determined for the mixture (carbon/nitrogen ratio of 20) based on the dry matter loss where the maximum amount of sewage sludge was used. On the other hand, maximum decomposition occurred at a carbon/nitrogen ratio of 23 for mixtures containing dairy manure. The increase in the use of olive pomace in mixtures had adverse effects on the decomposition process. The stabilization process in the mixture containing dairy manure lasted shorter than the mixtures containing sewage sludge.     

Modeling the effect of stratification on cemented layer formation in sulfide-bearing mine tailings

Reactive transport simulations have been applied to investigate possible effects of stratification on the potential of sulfide-bearing mine tailings to form protective cemented layers. The simulations are based on characteristic strata found at a German tailings site, including sulfide-enriched heavy mineral layers, mica-enriched silt layers, and homogeneously mixed layers. The simulated secondary phases (jarosite, gypsum, amorphous ferric arsenate, amorphous Fe hydroxide, alunite, amorphous silica, and kaolinite) are similar to those observed in the field. Using scanning electron microscope analyses of cemented layers, it has been observed that the pore area becomes disconnected if the porosity is decreased to values below 15%, which would indicate a strong decrease in permeability. Stratification was found to play a crucial role in cemented layer formation. Cemented layers are absent or insignificant in systems with a homogeneous distribution of Fe-bearing sulfides. They are extensively developed in systems with (a) an arsenopyrite-rich layer or (b) a mica-enriched layer situated immediately below an Fe-sulfide enriched layer. The modeling results have clearly demonstrated that the key processes operating in scenario (a) are very different from the key processes in scenario (b). In scenario (a), the oxidation of arsenopyrite is followed by the precipitation of amorphous ferric arsenate, which can be solely responsible for significant pore reduction. In scenario (b), the presence of a large amount of reactive aluminosilicates (e.g. biotite and Ca-bearing plagioclase) immediately below the Fe-sulfide rich layer appears to be crucial. Key processes are extensive formation of Acid Rock Drainage (ARD) followed by enhanced (pH-driven) weathering of aluminosilicates, resulting in the accumulation of secondary phases directly below the Fe-sulfide rich layer. In both scenarios, a cemented layer is formed that effectively retards the further downward movement of the oxidation front. The presented details on the role of stratification in the formation of cemented layers could be considered in the construction of mining heaps as a possible measure to stimulate natural attenuation.     

Biodegradation of phthalic acid esters in sewage sludge by composting with pig manure and rice straw

To comparatively study the biodegradation of phthalic acid esters (PAEs) in sewage sludge by composting with pig manure or with rice straw, four composting modes were designed: Mode 1 (sewage sludge + pig manure + intermittent aeration), Mode 2 (sewage sludge + pig manure + continuous aeration), Mode 3 (sewage sludge + rice straw + intermittent aeration) and Mode 4 (sewage sludge + rice straw + continuous aeration). Physicochemical parameters of composts were measured according to standard methods and PAEs were analyzed by gas chromatography coupled with mass spectrometry (GC/MS). The biodegradation of each PAE was also discussed. The results showed that Mode 1 was the best mode to biodegrade PAEs, which might be related to the wide class of indigenous microbial communities in pig manure and high efficiency of intermittent ventilation for providing oxygen. During the biodegradation process, di(2-ethylhexyl) phthalate was the most abundant and decisive for the removal of total PAEs. It showed a first-order kinetic degradation model. In conclusion, composting with pig manure could be suggested as an effective detoxification process for the removal of PAEs from sewage sludge, providing a safe end product.     

The effect of mineralogy on the mobility of heavy metals in mine tailings: a case study in the Samsanjeil mine,Korea

This study examined the chemical speciation and mobility of As and heavy metals in a tailings impoundment in Samsanjeil mine located in Gosung, Korea, as well as the factors affecting them. XRD, SEM, and 5-step sequential extraction were used to examine the samples at two sampling sites (NN and SN sites). The pH of the tailings decreased with increasing depth at the NN site (from 7.2 to 2.8), whereas no significant differences were observed at the SN site (8.1–8.8). The samples at the SN site showed a larger amount of calcite than those at the NN site, indicating that calcite plays an important role buffering the pH in the study sites. Jarosite was found only at the lower part of the NN site, where calcite was not found. The mineralogical observation of jarosite and calcite was also confirmed by SEM. The concentrations of As and heavy metals in the tailings were as follows: Cu > As > Zn > > Pb > Co > Cr > Ni > Cd. The total concentrations of Ni, Zn, Co, and Cd were higher at the SN site than those at the NN site. On the other hand, the concentrations of As and Cr existing as oxyanions were higher at the NN site, which can be explained by the mobility changes of those elements affected by pH variations. At the NN site, the fractions of heavy metals bound to the Fe/Mn oxides, except for As and Cr, decreased, and Cu, Zn, and Co showed an increasing fraction of exchangeable metals with increasing depth. This suggests that the pH and resulting surface charge of minerals, such as goethite and jarosite, are the dominant factors controlling the chemical speciation of metals. These results highlight the importance of mineralogy in controlling the mobility and possible bioavailability of heavy metals in tailings.     

Environmental risk evaluation of the use of mine spoils and treated sewage sludge in the ecological restoration of limestone quarries

The ecologic restoration criteria in areas degraded from extraction activities require making use of their mine spoils. These materials do not meet fertility conditions to guarantee restoration success and therefore, need the incorporation of organic amendments to obtain efficient substratum. Reducing the deficiencies in the organic material and restoration material nutrients with the contribution of treated sewage sludge is proposed in this work. This experiment was based on a controlled study using columns. The work was conducted with two mine spoils, both very rich in calcium carbonate. The first mineral, of poor quality, came from the formation of aggregates of crushed limestone (Z). The other residual material examined originated in limestone extraction, formed by the levels of interspersed non-limestone materials and the remains of stripped soils (D). Two treatments were undertaken (30,000 and 90,000 kg/ha of sewage sludge), in addition to a control treatment. The water contribution was carried out with a device that simulated either short-duration rain or a flooding irrigation system in order to cover the surface and then percolate through the soil. The collection of leached water took place 24 h after the applications. Different parameters of the leached water were determined, including pH, electrical conductivity, nitrate anions, ammonium, phosphates, sulphates and chlorides. The values obtained for each irrigation application are discussed, and the nitrate values obtained were very elevated.     

Geochemical and mineralogical aspects of sulfide mine tailings

Tailings generated during processing of sulfide ores represent a substantial risk to water resources. The oxidation of sulfide minerals within tailings deposits can generate low-quality water containing elevated concentrations of SO₄, Fe, and associated metal(loid)s. Acid generated during the oxidation of pyrite [FeS₂], pyrrhotite [Fe_(1−x)S] and other sulfide minerals is neutralized to varying degrees by the dissolution of carbonate, (oxy)hydroxide, and silicate minerals. The extent of acid neutralization and, therefore, pore-water pH is a principal control on the mobility of sulfide-oxidation products within tailings deposits. Metals including Fe(III), Cu, Zn, and Ni often occur at high concentrations and exhibit greater mobility at low pH characteristic of acid mine drainage (AMD). In contrast, (hydr)oxyanion-forming elements including As, Sb, Se, and Mo commonly exhibit greater mobility at circumneutral pH associated with neutral mine drainage (NMD). These differences in mobility largely result from the pH-dependence of mineral precipitation–dissolution and sorption–desorption reactions. Cemented layers of secondary (oxy)hydroxide and (hydroxy)sulfate minerals, referred to as hardpans, may promote attenuation of sulfide-mineral oxidation products within and below the oxidation zone. Hardpans may also limit oxygen ingress and pore-water migration within sulfide tailings deposits. Reduction–oxidation (redox) processes are another important control on metal(loid) mobility within sulfide tailings deposits. Reductive dissolution or transformation of secondary (oxy)hydroxide phases can enhance Fe, Mn, and As mobility within sulfide tailings. Production of H₂S via microbial sulfate reduction may promote attenuation of sulfide-oxidation products, including Fe, Zn, Ni, and Tl, via metal-sulfide precipitation. Understanding the dynamics of these interrelated geochemical and mineralogical processes is critical for anticipating and managing water quality associated with sulfide mine tailings.     

吉林红旗岭镍矿区尾矿地球化学特征研究

文章通过对红旗岭矿区尾砂数据的分析研究,对矿产资源的再度利用提出合理有效的方案,为矿产资源的二次开发开辟新的道路.在红旗岭尾矿库进行尾矿取样研究分析,测试尾砂中的元素含量,分析尾砂中元素的分布规律,依据工业品位要求,以及尾矿含水率等数据初步估算红旗岭矿区尾矿镍金属储量;对镍高品位值地段分析以及尾砂抽稀试验,为红旗岭尾矿...     

The management of sewage sludge by the water industry in England and Wales

Summary The legislative framework within which the disposal of sewage sludge is managed in England and Wales and the methods employed are outlined. Those factors which affect management decisions are analysed and consideration is given to the environmental implications of those decisions. Sewage processes and sludge disposal are considered, and the problems, especially those of heavy metal contamination, are addressed. An indication is given as to how the Water Services Companies are likely to implement the more stringent controls on disposal. Finally, the future of sludge management in England and Wales is discussed.Abbreviations BAT Best available technology - BATNEEC Best available technology not entailing excessive cost - BOD₅ Biochemical oxygen demand - BPEO Best practicable environmental option - CBI Confederation of British Industry - CEST Centre for Exploitation of Science and Technology - COD Chemical oxygen demand - CSC Customer Services Committee - DAF Dissolved air flotation - DG Director General - DoE Department of the Environment - DS Dried solids     

金川铜镍矿山尾矿砂酸溶性实验研究

为研究金川铜镍矿山酸性废水溶解尾矿砂实现综合治理废液与废固的可能性,进行了尾矿砂在硫酸中的溶解实验。结果表明,尾矿砂在硫酸浓度大于3mol/L、温度保持90℃以上并在液固比6.0下强力搅拌,能够较好地溶解于硫酸中,生成无定形二氧化硅;300℃的马弗炉焙烧4h有助于尾矿砂中绿泥石的溶解,对透闪石的溶解影响不大。尾矿砂中橄榄石、蛇纹石和透辉石较容易被硫酸溶解,透闪石、斜长石则比较难溶解,这与尾矿砂中矿物性质有密切关系。     

Mercury speciation in tailings of the Idrija mercury mine

Five hundred years of mercury (Hg) mining activity in Idrija, Slovenia caused widespread Hg contamination. Besides Hg emissions from the ore smelter, tailings have been found to be the major source of river sediment contamination. In the present study, solid phase binding forms and the aqueous mobility of Hg have been investigated in tailings of the Idrija Hg mine by means of a pyrolysis technique and aqueous Hg speciation. Results show that Hg binding forms differ with the age of the tailings due to the processing of different ores with different roasting techniques. In older tailings, the predominant Hg species is cinnabar (HgS), due to incomplete roasting, whereas in tailings of the 20th century the amount of cinnabar in the material decreased due to a higher efficiency of the roasting process and the increasing use of ores bearing native Hg. In younger tailings, metallic Hg (Hg⁰) sorbed to mineral matrix components such as dolomite and Fe-oxyhydroxides became the predominant Hg binding form in addition to unbound Hg⁰ and traces of HgO. Leaching tests show that in younger tailings high amounts of soluble Hg exist in reactive form. In older tailings most of the soluble Hg occurs bound to soluble complexes. It might be assumed that in the long term, matrix-bound Hg⁰ could be bound to humic acids derived from soils covering the tailings. This means that, despite the lower total Hg concentrations found in the younger tailings, the long-term risk potential of its mobile matrix-bound Hg⁰ is higher than that of older tailings bearing mostly immobile cinnabar.     

Competitive adsorption of trace elements in calcareous soils as affected by sewage sludge,poultry manure,and municipal waste compost

The competitive adsorption of trace elements is a key issue in assessing the mobility of trace elements in calcareous soils and can be affected by disposal of sewage sludge, municipal waste, and poultry manure. The effect of municipal sewage sludge, poultry manure, and municipal waste compost on the sorption of cadmium (Cd), copper (Cu), zinc (Zn), and nickel (Ni) in surface samples of three calcareous soils was studied. As the applied concentrations increased, Cu and Cd adsorption increased, while Zn and Ni adsorption decreased in all treatments. Based on the distribution coefficient (K _d) values and proportion of increase or decrease in metal adsorption, the selectivity sequence in control and amended soils found was Cu ≫ Cd ≫ Ni > Zn and Cu ≫ Cd ≫ Zn > Ni, respectively. In general, among control and amended soils, control soils showed the highest K _d for Cd, Cu, and Ni, while sludge, poultry manure, and composted waste-amended soils had lowest K _d for Cd, Cu, and Ni, respectively. In the case of Zn, composted waste-amended and control soils had highest and lowest K _d, respectively. The present experimental results indicated that the addition of organic amendments to these calcareous soils reduced the sorption of Cd, Cu, and Ni. Thus, the effects of preferential adsorption and organic matter should be considered in assessing the risk associated with applying sewage sludge, poultry manure, and composted material to calcareous soils.     

The concentration control of soluble copper in a mine tailings stream

Comparison of decreasing total copper content and increasing pH of an abandoned copper mine drainage stream to the stability fields of malachite, tenorite, and cupric hydroxide indicates that soluble copper is not lost by precipitation but by sorption on the stream sediments.     

Speciation and colloid transport of arsenic from mine tailings

In addition to affecting biogeochemical transformations, the speciation of As also influences its transport from tailings at inoperative mines. The speciation of As in tailings from the Sulfur Bank Mercury Mine site in Clear Lake, California (USA) (a hot-spring Hg deposit) and particles mobilized from these tailings have been examined during laboratory-column experiments. Solutions containing two common, plant-derived organic acids (oxalic and citric acid) were pumped at 13 pore volumes d⁻¹ through 25 by 500 mm columns of calcined Hg ore, analogous to the pedogenesis of tailings. Chemical analysis of column effluent indicated that all of the As mobilized was particulate (1.5 mg, or 6% of the total As in the column through 255 pore volumes of leaching). Arsenic speciation was evaluated using X-ray absorption spectroscopy (XAS), indicating the dominance of arsenate [As(V)] sorbed to poorly crystalline Fe(III)-(hydr)oxides and coprecipitated with jarosite [KFe₃(SO₄, AsO₄)₂(OH)₆] with no detectable primary or secondary minerals in the tailings and mobilized particles. Sequential chemical extractions (SCE) of <45 μm mine tailings fractions also suggest that As occurs adsorbed to Fe (hydr)oxides (35%) and coprecipitated within poorly crystalline phases (45%). In addition, SCEs suggest that As is associated with 1 N acid-soluble phases such as carbonate minerals (20%) and within crystalline Fe-(hydr)oxides (10%). The finding that As is transported from these mine tailings dominantly as As(V) adsorbed to Fe (hydr)oxides or coprecipitated within hydroxysulfates such as jarosite suggests that As release from soils and sediments contaminated with tailings will be controlled by either organic acid-promoted dissolution or reductive dissolution of host phases.     

尾矿中硫化物风化氧化模拟实验研究

为防治矿山尾矿造成环境污染，对方铅矿，闪锌矿，磁黄铁矿、黄铜矿，黄铁矿进行了风化氧化实验研究，结果显示，硫化物的氧化速率顺序为：方铅矿＞闪锌矿＞磁黄铁矿＞黄铜矿＞黄铁矿，侵蚀液pH值越低，硫化物氧化速率越大，有机物存在对硫化物氧化起缓冲和抑制作用。