Leaching Of Zn Research Articles

The effects of biochar and inorganic amendments on soil remediation in the presence of hyperaccumulator plant

Industrialization advances have led to an increase soil contamination by heavy metals. Among different technologies, in situ stabilization of metals combined with revegetation attracted attention. Therefore, this study aimed at comparing effects of biochars [rice husk biochar (RHB), maple leaves biochar (MLB)] and common inorganic amendments [red mud (RM), and steel slag (SS)] at different rates (0.5, 1, and 2% w/w) on leaching, and phytoavailability of metals (assessed using mustard green “Brassica juncea”). Soil pH in treated soils significantly (p < 0.01) increased, with the optimal pH ranges for plant growth observed in biochar-treated soils. The leaching of Cd, Cu, Pb, and Zn through soil significantly (p < 0.05) decreased in treated soils. Plant uptake and accumulation of Cd, Cu, Pb, and Zn decreased by 79–66, 13–19, 87–86, and 37–36% in RHB- and MLB-treated soils, respectively. Sequential extraction analysis pointed out that the major stabilization mechanism for metals using biochars involved the formation of organic and carbonate bonds, while for RM and SS was believed to involve the formation of inner sphere complexes with Fe/Al (hydr)oxides. The plant available fractions for Cd were generally higher than those for others. Overall, high dosage addition (2%) of each amendment offered the best compromise as it successfully reduced both leaching and phytoavailability of metals. Using MLB for the first time, showed promising results to immobilize metals with an increase in plant biomass.

Removal of metallic Al and Al/Zn alloys in MSWI bottom ash by alkaline treatment

In order to reduce the leaching of pollutants and remove the Al and Zn/Al alloy from municipal solid waste incineration bottom ash (MSWIBA), an optimized alkaline pre-treatment procedure was developed in this study. The influences of alkaline conditions on the removal rate of Al and Zn/Al alloy were investigated, including [OH]− concentration, temperature, particle size, liquid/solid ratio and treatment duration. The experimental results showed that the optimized alkaline pre-treatment conditions to efficiently remove the Al and Zn/Al alloy was by using a minimum of 1.0mol/l [OH]−, at 55°C and with a minimal liquid/solid ratio of 5. The removal rate of Al and Zn/Al alloy followed an S-shape curve, in which the slow beginning stage was attributed to the protection of the oxidation layer and the quenched product around the Al and Al/Zn alloy. After 3h of the optimized alkaline pre-treatment, the leaching of Cr, Cu, Pb and Zn of the treated MSWIBA was reduced by more than 90% of that of the original MSWIBA. The alkali-silica reaction test further indicated that the expansion of concrete prepared with the pre-treated MSWIBA was significantly reduced and there was no macro-crack or spalling damage on the surface of the tested specimens.

Direct Carbonation of Glycerol with CO2 Catalyzed by Metal Oxides.

Five metal oxides (ZnO, SnO2 , Fe2 O3 , CeO2 , La2 O3 ) were produced by the sol-gel method and tested in the direct carbonation of glycerol with CO2 . Initial tests with Fe2 O3 showed that the best reaction condition was 180 °C, 150 bar, and 12 h. The other oxides were evaluated at these conditions and were all active to the formation of glycerol carbonate. Zinc oxide was the most active catalyst, with a yield of 8.1 % in the organic carbonate. The catalytic activity decreased upon washing and drying the ZnO catalyst between the runs. Nevertheless, the activity is maintained if the ZnO is washed and calcined at 450 °C between the runs. FTIR and TGA results indicated the formation of ZnCO3 as the main cause of catalyst deactivation, which may be decomposed upon calcination of the material. No appreciable leaching of Zn was observed, indicating a truly heterogeneous catalysis.

Investigation of the effects of thermal treatment on the leachability of Zn and Mn from discarded alkaline and Zn[sbnd]C batteries

Spent alkaline and ZnC batteries are a potential source of Zn and Mn. This study reports on the effects of thermal treatment on the leachability of metals from such products. Black mass originating from alkaline and ZnC batteries was thermally treated under four different atmospheres: O2, N2, H2 and air at different temperatures (300–950 °C). Samples without prior thermal treatment and solid residues after thermal treatment were subsequently leached with H2SO4. Leaching of the samples without the thermal treatment was done to determine the reference leaching conditions, which were established to be 0.5 M H2SO4 at 25 °C for 60 min. Subsequently, samples which had been thermally treated were leached using the aforementioned reference conditions. The effect of thermal treatment on the leaching of Mn and Zn was studied to determine which conditions may improve or hinder subsequent hydrometallurgical processing of alkaline batteries. The use of O2 during the thermal treatment led to formation of ZnMn2O4, which inhibited effective leaching. ZnMn2O4 was decomposed in N2 atmosphere and in the presence of C, improving further dissolution of Mn. The use of H2 led to formation of Mn3O4. This compound showed low dissolution, being possible to be separated from impurities such as Fe, Ni and K by leaching with 0.5 M H2SO4. To increase the purity of recovered Mn3O4, oxalic acid was used as reduction agent. A final solid product, Mn3O4, with a purity of 99.95%, was obtained. Data provided by this research can lead to improvements of existing recycling processes, allowing for higher leaching efficiency of alkaline and ZnC battery materials. Also, overall material recovery rates can be increased by producing manganese oxide with high purity.

Effects and optimization of initial pH and sewage sludge compost content on leaching of lead and zinc in contaminated soil

We investigated the effects of initial pH (2≤pH0≤6) and sewage sludge compost content (5≤[SSC]≤25 g/kg) on leaching characteristics of lead (Pb) and zinc (Zn) in contaminated field soil. pH0 and [SSC] significantly affected the leaching of Pb and Zn in soils contaminated with them. The pH in the solution increased as reaction time and [SSC] increased. The leached amounts of Pb and Zn were highest at pH0=2 and increased with reaction time. As [SSC] increased, the leached amount of Pb decreased (50.4 mg/kg at control condition ([SSC]=0 g/kg); 22.9 mg/kg at [SSC]=25 g/kg at pH0=2) and the leached amount of Zn increased (20.1 mg/kg at [SSC]=0 g/kg; 31.7 mg/kg at [SSC]=25 g/kg at pH0=2). The change increased as pH0 decreased. Within the design boundaries, minimum leaching of Pb (14.7 mg/kg) occurred at pH0=5.1 and [SSC]=25 g/kg, and minimum leaching of Zn (5.0 mg/kg) occurred at pH0=5.1 and [SSC]=5 g/kg.

Evaluating solubility of Zn, Pb, Cu and Cd in pyrite cinder using leaching tests and geochemical modelling

Production of sulfuric acid by roasting of pyrite (Fe sulfide) produces a Fe rich waste product, pyrite cinder (or pyrite ash), which often contains high levels of trace metals such as Zn and Pb. The chemical forms of the metals and their solubility in these materials are poorly known. To evaluate the risks associated with pyrite cinder and manage cinder contaminated sites efficiently more knowledge on the chemical processes in pyrite cinder is needed. In this study the solubility of Zn, Pb, Cu and Cd in a pyrite cinder from Bergvik, Sweden, was investigated. The objectives were to (i) identify the solubility controlling processes for Zn, Pb, Cu, and Cd in the pH range 3–9, (ii) characterize the Fe (hydr)oxides present in these materials and (iii) to identify implications for management strategies of pyrite cinder contaminated sites. This was done using a combination of batch experiments, selective extractions, X-ray absorption spectroscopy and geochemical modelling. Hematite was identified as the dominating Fe mineral in the cinder. A geochemical model using generic binding parameters could describe the solubility of Zn, Cu and Cd in the cinder well, while Pb concentrations were generally underestimated. The modelling indicated that adsorption to Fe (hydr)oxides was the most important solubility controlling mechanism for all metals, except for Zn at pH > 6, where Zn minerals seemed to control the concentrations of Zn. To minimize leaching of Zn, Pb, Cu and Cd from cinder materials, remediation strategies should be focused on keeping the pH > 6.

Recovery of zinc and manganese from pyrometallurgy sludge by hydrometallurgical processing

In this contribution, a hydrometallurgical process is specifically developed to recover zinc (Zn), manganese (Mn) and lead (Pb) from the pyrometallurgical sludge produced in the steel manufacturing industries. The optimum conditions for Zn and Mn selective leaching from the pyrometallurgical sludge of Pompey have been already found. This process consists of six unit operations:1)Selective Zn leaching. At this stage, 80.8–100% of Zn is extracted.2)Selective Mn leaching, with two reductive leaching steps: fixed pH range from 3.5 to 4.2 and redox potential lower than 400 mV, using H2SO4 and Na2S2O5 as the reducing agent. In this step, 77.6–95.9% of Mn is recovered.3)Removal of aluminum (Al) and iron (Fe) from Zn leach liquor by chemical precipitation at pH 4.8 with NaOH.4)Removal of Al, Zn and Pb by sulfide precipitation (Na2S) from Mn leach liquor (2) at pH 5.6.5)Zn precipitation (as sphalerite) using twice the stoichiometry value of Na2S (considering the concentration of Zn).6)Mn precipitation (as rhodochrosite) at pH 8.5 using Na2CO3 as the precipitation agent.This process is tested with four different raw materials, which demonstrates its reliability.

Modeling desorption kinetics of the native and applied zinc in biochar-amended calcareous soils of different land uses

Soil components including organic matter (OM) are of vital importance in sorption/desorption kinetics of potentially toxic trace elements (PTEs), e.g., zinc (Zn). Nowadays, biochars as a source of OM have received increased attention because of their potential for improving soil properties. Effect of wheat straw biochar (0, 1.5 and 3% w/w) and zinc levels (0 and 10 mg Zn kg−1 soil as ZnSO4·7H2O) on Zn desorption kinetics was evaluated in an incubation experiments with agricultural, rangeland and forest soils. There was a rapid desorption rate during the first 2 h, followed by a slower rate during the next 14 h in all soil types. High rates of Zn desorption were observed in Zn-treated soils. In all soil types, biochar reduced Zn desorption, whereas, Zn increased it. The highest amounts of Zn desorption in both no Zn-treated and Zn-treated soils corresponded to the forest soil followed by the rangeland and agricultural soils. The simple Elovich and two-constant rate models were the best models to describe Zn desorption from the soils. Biochar decreased the release of Zn to the soil solutions. Therefore, it may reduce the probable excessive amount of Zn uptake by plant root, transfer to food chain, Zn leaching to surface and subsurface waters and their possible risks to human health. These issues should be considered in management practices for different land uses under various Zn application strategies. Furthermore, evaluation of other levels/sources of biochar and Zn on desorption kinetics of Zn in soils of various land use types is recommended.

Comparison of different MSWI fly ash treatment processes on the thermal behavior of As, Cr, Pb and Zn in the ash

To reduce heavy metal leaching and stabilize municipal solid waste incineration (MSWI) fly ash, different methods and combination of methods were tested: water washing, electrodialytic separation and thermal treatment at 1000°C. A comparison of heavy metal concentration and leaching levels of As, Cr, Pb and Zn for the different untreated and treated ashes was made. The results showed that minimizing leaching to meet the limiting values of the all the studied heavy metals can be obtained at the same time by combining water washing, electrodialytic separation and thermal treatment. The ash subjected to this combination had lower Cr than the ash solely subjected to thermal treatment or subjected to water washing prior to thermal treatment. The electrodialytic separation (EDS) of the washed ash lowered pH from alkaline to acidic, which resulted in elevated leaching of Cd and Zn, while the Cr leaching was reduced. Up to 58.6% of Zn and 5.5% of Pb were extracted by EDS compared to less than 0.6% extraction by water washing. During thermal treatment of the EDS treated ash, the ash was re-alkalized. Due to solidification and possibly evaporation, most heavy elements left in the thermally treated ash were stabilized and immobilized. However, leaching of As and/or Cr was still problematic and did not meet the limit value for the thermally treated ash being recycled in construction work. The removal of Ca and decomposition of Ca oxides and minerals during EDS was linked to the leaching patterns of As and Cr after thermal treatment.

Municipal solid waste incineration (MSWI) fly ash washing pretreatment by biochemical effluent of landfill leachate: a potential substitute for water

ABSTRACTSulfate-rich biochemical effluent of landfill leachate (BEL) resulting from aged refuse bioreactor was employed to wash municipal solid waste incineration (MSWI) fly ash. The dechlorination ability of BEL was found to be nearly equivalent to redistilled water (RW), and the concentrations of lead (Pb) and zinc (Zn) in the washing solution resulting from the BEL washing process were lower than that of the RW washing process. Fourier transform infrared (FTIR) analysis indicated that the formation of calcium sulfate and hydroxides in fly ash after BEL washing and their entrapping function could significantly inhibit the leaching of Pb and Zn. Besides, toxicity characteristic leaching procedure (TCLP) tests showed that the BEL washing treatment did not increase the risk of heavy metals leaching from fly ash, and the leaching concentrations of Pb, Zn, copper (Cu) and cadmium (Cd) of BEL washed fly ash were lower than that of RW washed fly ash, which suggested BEL washing treatment could slightly immobilize heavy metals in fly ash. For MSWI fly ash dechlorination, our present results indicated that BEL used in this batch experiment could be a potential substitute for water.

Heavy Metal Leaching as Affected by Long-Time Organic Waste Fertilizer Application.

The recycling of urban waste products as fertilizers in agriculture may introduce contaminants such as heavy metals into soil that may leach and contaminate groundwater. In the present study, we investigated the leaching of heavy metals from intact soil cores collected in the long-term agricultural field trial CRUCIAL. At the time of sampling, the equivalent of >100 yr of urban waste fertilizers following Danish legislation had been applied. The leaching of Cu was significantly increased in the treatments receiving organic waste products compared with the unfertilized control but remained below the permissible level following Danish drinking water guidelines. The leaching of Cu was controlled primarily by the topsoil Cu content and by the leaching of dissolved organic carbon (DOC) but at the same time significantly correlated with leaching of colloids in soils that had not received fertilizer or had received an organic fertilizer with a low concentration of Cu. The leaching of Zn, Cd, and Co was not significantly increased in urban waste-fertilized treatments. The leaching of Mo was elevated in accelerated waste treatments (both agricultural and urban), and the leaching of Mo was linked to the leaching of DOC. Since leaching of Cr and Pb was strongly linked to the level of colloid leaching, leaching of these metals was reduced in the urban waste treatments. Overall, the results presented should not raise concern regarding the agricultural use of urban waste products in agriculture as long as the relevant guidelines are followed.

Effects of SiO2, Al2O3 and Fe2O3 on leachability of Zn, Cu and Cr in ceramics incorporated with electroplating sludge

Large amounts of electroplating sludge generated in electroplating industry require recycling or alternative recovery solutions to minimize environmental impact caused by the waste. The use of electroplating sludge as raw materials in the production of building materials is a feasible alternative to valorize this waste. In this study, the effects of SiO2, Al2O3 and Fe2O3 on the leachability of heavy metals (i.e. Zn, Cu and Cr(III)) during firing ceramics with the addition of electroplating sludge were examined. The results showed that Zn preferably combined with Cr(III) to form ZnCr2O4 in comparison to the formation of ZnAl2O4 and ZnFe2O4, and Zn could also be incorporated into Zn2SiO4 structure. However, Zn spinel structure have better resistance against acid attack comparing with Zn2SiO4. Cu can only be transformed into spinel phases of CuAl2O4 and CuFe2O4. SiO2, Al2O3 and Fe2O3 make less contributions to the immobilization of Cr(III). The presence of CaO severely impacted the formation of spinel phases, especially for Cr spinel. Moreover, Cr(III) would be oxidized into Cr(VI) due to the presence of CaO. It appears that the presence of SiO2 may inhibit the oxidation of Cr(III) comparing with Al2O3 and Fe2O3, which can be attributed to the interaction of CaO with SiO2 decreasing the amount of CaO. This study can provide a basic understanding for the leachability of Zn, Cu and Cr during the use of solid waste containing heavy metals in the production of clay bricks or ceramics.

Potential value of phosphate compounds in enhancing immobilization and reducing bioavailability of mixed heavy metal contaminants in shooting range soil

Shooting range soils contain mixed heavy metal contaminants including lead (Pb), cadmium (Cd), and zinc (Zn). Phosphate (P) compounds have been used to immobilize these metals, particularly Pb, thereby reducing their bioavailability. However, research on immobilization of Pb’s co-contaminants showed the relative importance of soluble and insoluble P compounds, which is critical in evaluating the overall success of in situ stabilization practice in the sustainable remediation of mixed heavy metal contaminated soils. Soluble synthetic P fertilizer (diammonium phosphate; DAP) and reactive (Sechura; SPR) and unreactive (Christmas Island; CPR) natural phosphate rocks (PR) were tested for Cd, Pb and Zn immobilization and later their mobility and bioavailability in a shooting range soil. The addition of P compounds resulted in the immobilization of Cd, Pb and Zn by 1.56–76.2%, 3.21–83.56%, and 2.31–74.6%, respectively. The reactive SPR significantly reduced Cd, Pb and Zn leaching while soluble DAP increased their leachate concentrations. The SPR reduced the bioaccumulation of Cd, Pb and Zn in earthworms by 7.13–23.4% and 14.3–54.6% in comparison with earthworms in the DAP and control treatment, respectively. Bioaccessible Cd, Pb and Zn concentrations as determined using a simplified bioaccessibility extraction test showed higher long-term stability of P-immobilized Pb and Zn than Cd. The differential effect of P-induced immobilization between P compounds and metals is due to the variation in the solubility characteristics of P compounds and nature of metal phosphate compounds formed. Therefore, Pb and Zn immobilization by P compounds is an effective long-term remediation strategy for mixed heavy metal contaminated soils.

Simulated upland placement of estuarine dredged materials

Placement of estuarine dredged materials on the land surface can result in severe environmental issues if acid sulfate conditions develop. In this study, upland placement of marine dredged material was simulated using a mesocosm experiment. Dredged materials were sampled from eight low energy and high energy subaqueous soil-landscape units of four estuaries in Rhode Island. Soils were mapped in the low energy landscape units (i.e. coves and bottoms) as Sulfiwassents and in the high energy units (i.e. deltas and fans) as Psammowassents. Dredged materials were characterized for various physical and chemical properties, placed into mesocosms, and exposed to natural climatic conditions outside. In addition, high energy and low energy materials were mixed at ratios of 20:1, 10:1, 5:1, and 2.5:1 and placed in mesocosms. Mesocosm leachate was collected and analyzed for pH, conductivity, and sulfate content for over 2years (one year for the mixed mesocosms). Dredged materials ranged from sand to silt loam textures with the Sulfiwassents having finer textures and higher levels of carbon and calcium carbonates. Inorganic sulfide concentrations ranged from 56 to 3410μgg−1, with an average of 228μgg−1 for the Psammowassents and 2319μgg−1 for Sulfiwassents. Concentrations of Zn in the Sulfiwassent materials decreased by more than half after 2-years suggesting leaching of Zn during oxidation of the dredged materials. Leachate from low energy Sulfiwassents showed a large drop in pH (pH≤4.0) associated with sulfide oxidation and creation of acid sulfate conditions, while leachate from coarser textured Psammowassents increased in pH to >8.0, presumably from the formation of salts. These conditions generally persisted for the duration of the experiment. Salts washed out of the dredged material fairly quickly such that leachate conductivities reached <5dSm−1 in 10months. Sulfate content of the leachate varied for the first 18months with the Sulfiwassent materials having higher levels and taking longer to wash out. Leachate from mixing as little as 5% Sulfiwassent with Psammowassent materials resulted in acid sulfate leachate (pH<4) in less than a year. Our results suggest that developing soil interpretations for upland placement of dredged materials of estuarine subaqueous soils should be focused on limitations as the result of creation of acid sulfate conditions and leaching of metals for Sulfiwassents and potentially high pH values for Psammowassents.

Extraction of manganese and zinc from their compound ore by reductive acid leaching

Comprehensive utilization of low grade manganese–zinc compound ore containing lead and silver with a method of reductive acid leaching was studied. According to the ϕ–pH diagram of Mn–Zn–H2O system, Mn and Zn can be leached simultaneously in the pH range of –2 to 5.61. The results showed that both hydrogen peroxide and sucrose were effective reductants which could intensify the simultaneous leaching of Mn and Zn into leachate as well as enrich Pb and Ag in the residue. 95.88% of Mn and 99.23% of Zn were extracted when the compound ore was leached with hydrogen peroxide in sulfuric acid media, meanwhile the contents of Pb and Ag in the residue were enriched to 13.21% and 489.36 g/t, respectively. When sucrose was used as the reductant, the leaching efficiencies of Mn and Zn separately achieved 98.26% and 99.62%, and contents of Pb and Ag in the residue were as high as 13.92% and 517.87 g/t, respectively.

Leachate analysis of green and fired-clay bricks incorporated with biosolids

The substantial increase in biosolids production throughout the world requires sustainable routes for reuse. This study describes the leaching behaviour of potentially hazardous metals from the green and fired bricks incorporating four different biosolids samples from the Eastern treatment plant (ETP) and Western treatment plant (WTP) in Melbourne. The biosolids samples were characterized by XRD, XRF, TGA, particle size distribution, and organic content. The leaching of As, Ag, Ba, Be, Cd, Cr, Cu, Mo, Ni, Pb, Sb, Se, and Zn was evaluated for both the green and the fired bricks according to the Toxicity characteristic leaching procedure (TCLP) and the Australian bottle leaching procedure (ABLP). The leaching of heavy metals from both the green and the fired bricks was compared to investigate the effect of firing on the leaching capability of bricks. The results showed that the leaching of heavy metals from fired bricks was significantly lower than that for the green bricks. The ABLP concentrations of heavy metals were higher than those found using the TCLP method, mainly due to the higher specific surface area of the particles used in the ABLP method. Moreover, bricks were evaluated by the technological properties, such as compressive strength, density and water absorption.

Extraction of Ga and Ge from zinc refinery residues in H2C2O4 solutions containing H2O2

A new oxalic acid (H2C2O4) and hydrogen peroxide (H2O2) based extraction process was developed to recover valuable metals - in particular Ga and Ge - from the zinc refinery residues. H2C2O4 and H2O2 leaching studies indicated that the selective leaching of metals in the residues, that primarily contain Zn, Cu, Fe, SiO2, Ga and Ge, can be achieved. Under the optimal leaching conditions ([H2C2O4]=110g/L, [H2O2]=0.12mol/L, L/S ratio=8, T=40°C and t=30min), 99.32% of the Ga, 98.86% of the Ge and 30.25% of the Fe were leached out, whereas the leaching of Zn, Cu and Si only reached 0.30%, 0.82% and 0.43%, respectively. Concerning leachate purification, 98.31% of the iron could be removed in the form of FeC2O4·2H2O with minor losses of Ga and Ge (1.08% and 0.68%) using an ultrasound-assisted iron powder replacement method under optimal conditions. The Ga (99.36%) and Ge (99.89%) were subsequently extracted by tri(octyl-decyl)amine (N235). After extraction, the loaded organic phase was stripped of Ga (98.91%) and Ge (99.21%) into separate solutions using sequential treatments of 2mol/L H2SO4 and 4mol/L NaOH respectively. Based on these results, a process flow sheet of efficient separation and recovery of Ga and Ge is presented.

The speciation, leachability and bioaccessibility of Cu and Zn in animal manure-derived biochar: effect of feedstock and pyrolysis temperature

Biochars derived from animal manures may accumulate potentially toxic metals and cause a potential risk to ecosystem. The synchrotron-based X-ray spectroscopy, sequential fractionation schemes, bioaccessibility extraction and leaching procedure were performed on poultry and swine manurederived biochars (denoted PB and SB, respectively) to evaluate the variance of speciation and activity of Cu and Zn as affected by the feedstock and pyrolysis temperature. The results showed that Cu speciation was dependent on the feedstock with Cu-citrate-like in swine manure and species resembling Cu-glutathione and CuO in poultry manure. Pyrolyzed products, however, had similar Cu speciation mainly with species resembling Cu-citrate, CuO and CuS/Cu2S. Organic bound Zn and Zn3(PO4)2-like species were dominant in both feedstock and biochars. Both Cu and Zn leaching with synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) decreased greatly with the rise of pyrolysis temperature, which were consistent with the sequential extraction results that pyrolysis converted Cu and Zn into less labile phases such as organic/sulfide and residual fractions. The potential bioaccessibility of Zn decreased for both the PB and SB, closely depending on the content of non-residual Zn. The bioaccessibility of Cu, however, increased for the SB prepared at 300°C–700°C, probably due to the increased proportion of CuO. Concerning the results of sequential fractionation schemes, bioaccessibility extraction and leaching procedure, pyrolysis at 500°C was suggested as means of reducing Cu/Zn lability and poultry manure was more suitable for pyrolysis treatment. Open image in new window

Fate of copper, nickel and zinc after biogas digestate application to three different soil types.

Soil application of organic residues from anaerobic digestion of municipal food waste and/or sewage sludge may introduce considerable amounts of heavy metals into the environment. In a column leaching experiment, mobility and release of Cu, Ni and Zn were investigated in three contrasting soils (sand, silt, loam) fertilized with biogas digestates of different origin. The effect of commercial digestates, based on food waste and sewage sludge, was compared to that of experimental digestates based on animal manure and whey permeate with or without fish ensilage, as well as untreated manure, mineral fertilizer and an untreated control. Manure and digestates were added to the columns as fresh material at equal amounts of available nitrogen. The experiment simulated high-intensity rainfall over a period of 7days. In general, soil treated with the commercial digestates with higher original metal content showed less environmental impact in terms of Ni, Cu and Zn leaching than that treated with experimental digestates with lower original metal content and less than when animal manure or mineral fertilizer was applied. Although effects of digestate application on metal mobility in soils were seen in conditions of extreme precipitation, the leached concentrations of metals were below limitations published by the WHO but still significantly higher than that measured for control soils.

Comparison of mechanical and leaching behaviours of pulverised fuel ash/low-grade magnesium oxide-cement blended stabilised/solidified baghouse dust

This paper investigates the leaching potential of heavy metals present in stabilised/solidified (S/S) electric arc furnace dust (EAFD). Granular leaching test results showed that Mo was effectively stabilised by Portland cement type I (CEMI) and MgO at 1:2:7 and 3:12:35 ratios. Monolithic leaching test results showed that pulverised fuel ash (PFA) stabilised Zn and Pb but not Mo and Cl. MgO was highly effective in reducing Zn leaching. X-ray diffraction analysis revealed the presence of zinc ferrite in the solidified EAFD products which explains the excellent immobilisation of Zn. The leaching mechanisms analysis demonstrated that few S/S samples exhibited a leaching behaviour dominated by diffusion with the majority displaying a leaching mode dominated by depletion. Although the monoliths’ physical integrity was maintained, Pb, Cl and Mo were not effectively immobilised with PFA and MgO-based systems based on the current granular and monolith leaching test protocols.