Total Leaching Research Articles

Nanoparticles within WWTP sludges have minimal impact on leachate quality and soil microbial community structure and function

One of the main pathways by which engineered nanoparticles (ENPs) enter the environment is through land application of waste water treatment plant (WWTP) sewage sludges. WWTP sludges, enriched with Ag and ZnO ENPs or their corresponding soluble metal salts during anaerobic digestion and subsequently mixed with soil (targeting a final concentration of 1400 and 140 mg/kg for Zn and Ag, respectively), were subjected to 6 months of ageing and leaching in lysimeter columns outdoors. Amounts of Zn and Ag leached were very low, accounting for <0.3% and <1.4% of the total Zn and Ag, respectively. No differences in total leaching rates were observed between treatments of Zn or Ag originally input to WWTP as ENP or salt forms. Phospholipid fatty acid profiling indicated a reduction in the fungal component of the soil microbial community upon metal exposure. However, overall, the leachate composition and response of the soil microbial community following addition of sewage sludge enriched either with ENPs or metal salts was very similar.

Earthworm activities increase the leaching of salt and water from salt-affected agricultural soil during the wet–dry process under simulated rainfall conditions

The objectives of this study were to (1) evaluate earthworm-induced leaching of water and salt from salt-affected agricultural soils with constant and fluctuating soil moisture conditions and (2) determine the effects of earthworms on the distribution of soil salt in casts, burrow walls, and surrounding soils responsible for salt leaching. Soils were kept in mesocosms at constant moisture (CM) or underwent one wet–dry process (WD). Each soil moisture treatment had three earthworm treatments, including (1) inoculation with high abundance of earthworms (five endogeic Aporrectodea trapezoides), (2) inoculation with moderate abundance of earthworms (three endogeic A. trapezoides), and (3) no earthworm treatment. The presence of earthworms significantly increased total leaching water volume compared to the same treatment without earthworms in both moisture treatments. In the treatment following the wet–dry process, more than 65 % of water leaching occurred during the rainfall event, whereas in the treatment following constant moisture, more than 60 % of water leaching occurred after the rainfall event. The presence of earthworms produced a higher salt amount in the leaching water than the same moisture treatment without earthworms, but only the low number of earthworms (three endogeic A. trapezoides) caused a significantly higher total amount of leached salt than the same moisture treatment without earthworms. The percentage of leached salt in leaching water during the rainfall event ranged from 75.31 to 79.93 % in the wet–dry treatment and from 41.28 to 50.65 % in the constant moisture treatment. The wet–dry process significantly increased the total amount of leached salt from salt-affected agricultural soil compared to the constant moisture treatment when earthworms were present, which may be due to the significantly higher electrical conductivity of saturation extract (ECe) of earthworm casts than those of burrow walls and surrounding soils in the 0- to 10-cm soil layer.

The role of subsoil as a source or sink for phosphorus leaching.

The importance of subsoil features for phosphorus (P) leaching is frequently mentioned, but subsoil effects are still poorly documented. This study examined whether the subsoil of four agricultural Swedish soils (two sand and two clay) functioned as a source or sink for P leaching by measuring P leaching from intact soil columns with topsoil (1.05 m deep) and without topsoil (0.77 m deep) over 3 yr. One sandy soil with high topsoil P content (Olsen P, 84 mg kg) and high subsoil sorption capacity (P sorption index [PSI], 3.7 mmol kg) had low leaching of dissolved reactive P (DRP) from full-length and subsoil lysimeters (0.12 and 0.08 kg ha yr, respectively). The other sandy soil, with high Olsen P content in the topsoil and subsoil (27 and 19 mg kg, respectively) and low PSI in the subsoil (1.4 mmol kg), had high DRP leaching from full-length and subsoil lysimeters (3.33 and 3.29 kg ha yr, respectively). High P content at depth (Olsen P, 21 mg kg) in one clay soil resulted in relatively higher subsoil DRP contribution (89%) to total leaching than observed in the other clay soil (71%). These results indicate that the subsoil can act as source or sink for P leaching, depending on P content, degree of P saturation, and P sorption capacity, and therefore subsoil properties should be considered when selecting mitigation measures to reduce P leaching.

Leaching losses of Nitrogen, Phosphorus and Potassium from the sandy loam soil of old Brahmaputra floodplain (AEZ-9) under continuous standing water condition

An experiment was conducted at the net house of the Department of Soil Science, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh during February to June (boro season) of 2009. The objective was to find out the leaching loss of N, P, and K in the Old Brahmaputra Floodplain Soil under continuous standing water (CSW) condition. The soil was sandy loam in texture having pH 6.6, total N 0.08%, available P 7.00 mg/kg, exchangeable K 0.07 me/100g soil, and available S 7.5 mg/kg. The experiment was laid out in completely randomized design with three replications. There were six treatments, such as T0 (control), T1 (N120 P25 K60 S20 recommended dose), T2 (N180 P37 K90 S30 kg/ha i.e., 150% of the recommended dose), T3 (75% N of T1 from chemical fertilizer and 25% N from cowdung 2.5 t/ha and PKS of recommended dose from chemical fertilizer on the basis of PKS content in cowdung), T4 (as T1 but N109 kg/ha from USG) and T5 (as T1 but N applied as foliar spray). The nutrients P, K, and S were applied as basal dose in the pots while urea was applied in three equal splits except T4 and T5. One USG per pot was placed after 7 days of transplanting in T4. In T5, urea was applied as foliar spray at 10 days interval. Leachates from individual pots were collected at 15 days intervals to determine the amount of loss of NPK. Results showed that leaching loss of NPK in the sandy loam soil under CSW condition varied widely due to different treatments over time. The total leaching loss of N, P, and K during the growing season varied from 22.23 to 91.21, 0.063 to 1.95, and 35.22 to 42.01 kg/ha, respectively. Application of chemical fertilizer at higher rates resulted in greater loss of nutrients. Integrated approach of fertilizer management could minimize such losses to a great extent. Application of N in the form of USG reduced the N loss significantly. DOI: http://dx.doi.org/10.3329/bjar.v39i3.21987 Bangladesh J. Agril. Res. 39(3): 437-446, September 2014

Heavy Metals Leaching from the Incinerator Bottom Ash Used for Road Pavement

This study analyzed the bonding strength of each kind of heavy metals by simulating the influence of pressure and acid rain when recycling incineration bottom ash from real factory as road building materials. Experimental results indicated that total leach quantity of heavy metals gradually reduced over time. After contrasting results of sequential extraction, it can be found that bonding forms of most heavy metals are organic matter state and residue state which are difficult to be leached, while the first three states are easy to be leached. The quantity of leach increased at the beginning due to the metal bonding of the first three states. In addition, compared with heavy metals in high pH value (2.88), leach quantity of all heavy metals is the largest in low pH value (1.1). However, different operating pressures have little effect on the leach of heavy metals. But if the aggregate size of bottom ash changes, it can be found that the large specific surface area of bottom ash with fine aggregate size is beneficial for the bottom ash to contact with filter liquor. Hence, leach concentration of heavy metals is higher than the bottom ash with coarse aggregate.

The Effect of the Calcium Leaching on the Microstructure and Rupture Strength of CA Mortar

This paper deals with the effect of calcium leaching on the microstructure and rupture strength of cement asphalt (CA) mortar. It is conducted by an accelerated experiment method with species obtained from construction site. Results show that the leaching process mainly contains a total leaching of CaOH2 (CH) and some other cement hydrations. The leaching is proved by the “portlandite dissolution front” on the cross-section of species using a reagent of phenolphthalein. As time goes, the species are continually leached, and then the loss of mass and porosity ratio are obviously increased. Fick’s law can describe the relationship between leaching depth and time very well. The loss of mass and increasing of porosity ratio respond to the shrinking of mechanical properties of CA mortar.

Binding of Industrial Deposits of Heavy Metals and Arsenic in the Soil by 3-Aminopropyltrimethoxysilane

Abstract The results of the research studies concerning binding of heavy metals and arsenic (HM+As), occurring in soils affected by emissions from Głogów Copper Smelter and Refinery, by silane nanomaterial have been described. The content of heavy metals and arsenic was determined by AAS and the effectiveness of heavy metals and arsenic binding by 3-Aminopropyltrimethoxysilane was examined. The total leaching level of impurities in those fractions was 73.26% Cu, 74.7% – Pb, 79.5% Zn, 65.81% – Cd and 55.55% As. The studies demonstrated that the total binding of heavy metals and arsenic with nanomaterial in all fractions was about as follows: 20.5% Cu, 9.5% Pb, 7.1% Zn, 25.3% Cd and 10.89% As. The results presented how the safety of food can be cultivated around industrial area, as the currently used soil stabilization technique of HM by soil pH does not guarantee their stable blocking in a sorptive complex.

Nitrogen and phosphorus leaching losses from intensively managed paddy fields with straw retention

A field experiment was carried out for three years to examine the concentrations of NH4+-N, NO3−-N and dissolved total phosphorus (TP) in leachates and cumulative leaching losses in rice fields with straw retention under different rates of fertilizer N application. With straw retention, the percolation rate had a significant (p<0.05) negative exponential relationship with the day after rice transplanting, accounting for an average 2.57mmd−1. NH4+-N and NO3−-N concentration in percolation increased with increasing of N fertilizer application rate. Compared to the control (without straw or fertilizer), the wheat straw incorporation with nil N fertilizer decreased the concentration of NH4+-N and NO3−-N but promoted TP concentration. Cumulative inorganic N (NH4+-N+NO3−-N) and P losses were about 14.4 and 0.53kgha−1, accounting for 5.6% and 3.5% of N and P fertilizer applied. NH4+-N leaching losses accounted for 62–97% of the total leaching of inorganic N. Nitrogen leaching losses occurred mainly at the basal fertilizer application stage, accounting for 76.8% of total N leaching. Straw retention reduced the N leaching losses because the straw can enhance microbial N immobilization due to its high C:N ratio. However, the mechanism of straw incorporation impacts on N and P leaching requires more detailed study.

Changes in N leaching and crop production as a result of measures to reduce N losses to water in a 6‐yr crop rotation

AbstractThe effects of various measures introduced to increase nitrogen (N)‐use efficiency and reduce N losses to water in a 6‐yr crop rotation (winter wheat, spring barley, green manure, winter wheat, spring barley, spring oilseed rape) were examined with respect to N leaching, soil mineral N (SMN) accumulation and grain yield. An N‐use efficient system (NUE) with delayed tillage until late autumn and spring, direct drilling of winter wheat, earlier sowing of winter and spring crops and use of a catch crop in winter wheat was compared with a conventional system (CON) in a field experiment with six separately tile‐drained plots in south‐western Sweden during the period 1999–2011 (two crop rotation cycles). Total leaching of NO3‐N from the NUE system was significantly 46 and 33% lower than in the CON system during the first and second crop rotation cycle, respectively, with the most pronounced differences apparently related to management strategies for winter wheat. Differences in NO3‐N leaching largely reflected differences in SMN during autumn and winter. There was a tendency for lower yields in the NUE system, probably due to problems with couch grass. Overall, the measures for conserving N, when frequently used within a crop rotation, effectively reduced NO3 concentrations in drainage water and NO3‐N leaching losses, without severely affecting yield.

Rare earth elements recycling from waste phosphor by dual hydrochloric acid dissolution

This paper is a comparative study of recycling rare earth elements from waste phosphor, which focuses on the leaching rate and the technical principle. The traditional and dual dissolution by hydrochloric acid (DHA) methods were compared. The method of dual dissolution by hydrochloric acid has been developed. The Red rare earth phosphor (Y0.95Eu0.05)2O3 in waste phosphor is dissolved during the first step of acid leaching, while the Green phosphor (Ce0.67Tb0.33MgAl11O19) and the Blue phosphor (Ba0.9Eu0.1MgAl10O17) mixed with caustic soda are obtained by alkali sintering. The excess caustic soda and NaAlO2 are removed by washing. The insoluble matter is leached by the hydrochloric acid, followed by solvent extraction and precipitation (the DHA method). In comparison, the total leaching rate of the rare earth elements was 94.6% by DHA, which is much higher than 42.08% achieved by the traditional method. The leaching rate of Y, Eu, Ce and Tb reached 94.6%, 99.05%, 71.45%, and 76.22%, respectively. DHA can decrease the consumption of chemicals and energy. The suggested DHA method is feasible for industrial applications.

Study on leaching of molybdenum and nickel from Ni–Mo ore using sodium chlorate

The leaching of molybdenum and nickel from a Ni–Mo ore was investigated by acidic oxidative leaching with sodium chlorate followed by caustic leaching of the acid leach residue. The results indicated that the sulphides of nickel and molybdenum in the Ni–Mo ore were oxidised and dissolved in the solution. The molybdenum remaining in the residue was further recovered by direct caustic leaching. The leaching of nickel and molybdenum reached 92 and 60% respectively, with sodium chlorate consumption of 60 g per 100 g ore and hydrochloric acid consumption of 0·52 mol per 100 g ore at a L/S ratio of 3∶1 and 90°C for 2 h. After caustic leaching of the acid leach residue with sodium hydroxide consumption of 45 g per 100 g dried residue at a L/S ratio of 3∶1 and 40°C for 15 min, the total leaching of molybdenum increased to 96%. A conceptual process flowsheet for the leaching of the Ni–Mo ore has been developed.On a examiné le lessivage du molybdène et du nickel à partir d’un minerai de Ni-Mo, par lessivage acide oxydant avec du chlorate de sodium suivi par lessivage caustique du résidu d’attaque acide. Les résultats indiquaient que les sulfures de nickel et de molybdène du minerai de Ni–Mo étaient oxydés et dissous dans la solution. Le molybdène du résidu était davantage récupéré par lessivage caustique direct. Le lessivage du nickel et du molybdène atteignait 92 et 60%, respectivement, avec une consommation de chlorate de sodium de 60 g par 100 g de minerai et une consommation d’acide chlorhydrique de 0·52 mol par 100 g de minerai avec un rapport de L/S de 3∶1 à 90°C pendant 2 h. Après le lessivage caustique du résidu d’attaque acide avec une consommation d’hydroxyde de sodium de 45 g par 100 g de résidu séché avec un rapport de L/S de 3∶1 à 40°C pendant 15 min, le lessivage total du molybdène augmentait à 96%. On a développé un schéma de procédé conceptuel pour le lessivage du minerai de Ni–Mo.

Fate of fertilizer 15N in intensive ridge cultivation with plastic mulching under a monsoon climate

Reducing nitrogen (N) leaching to groundwater requires an improved understanding of the effect of microtopography on N fate. Because of the heterogeneity between positions, ridge tilled fields, frequently used in intensive agriculture, should be treated as two distinct management units. In this study, we measured N dynamics in plastic-mulched ridges and bare furrows with the goal of developing more sustainable agricultural practices with optimal gains, namely crop production versus limited impacts on water quality. We investigated: (1) biomass production; (2) crop N uptake; (3) N retention in soil; and (4) N leaching using 15N fertilizer in a radish crop. Broadcast mineral N fertilizer application prior to planting resulted in high total leaching losses (of up to 390 N kg ha−1). The application of plastic mulch in combination with local fertilizer management did not help to reduce N leaching. At all fertilizer N rates, the mean NO3 − concentrations in seepage water were found to be above the WHO drinking water standard of 50 mg NO3 − l−1. To reduce NO3 − leaching, we recommend: (1) decreasing the fertilizer N rates to a maximum of 150 kg N ha−1; (2) applying fertilizer N in 3–4 split applications according to the plant’s N needs; (3) applying fertilizer N to the ridges (after their formation) to avoid losses from the furrows; and (4) increasing the soil organic matter content to enhance the water and nutrient retention by covering the furrows with plant residues.

Impact of Biochar Enriched with Dairy Manure Effluent on Carbon and Nitrogen Dynamics

Amending soils with biochar can have multiple environmental benefits, including improvement in soil physicochemical properties, carbon sequestration, reduction in leaching losses of essential nutrients, and reduction in greenhouse gas (GHG) emissions. This study was conducted to determine the effect of enriched biochar amendments on leaching losses of essential nutrients and GHG emissions from soil. The enriched biochar was prepared by shaking biochar with dairy manure effluent for 24 h, which increased the C and N concentration of biochar by 9.3 and 8.3%, respectively. Incubation and leaching experiments were conducted for 8 wk with three treatments: soil, soil + 1% biochar, and soil + 1% enriched biochar. Amendment with biochar and enriched biochar relative to unamended soil resulted in 68 and 75% reduction in net nitrification, 221 and 229% reduction in net ammonification, 67 and 68% reduction in cumulative CO flux, respectively, and 26% reduction in cumulative NO flux for both biochar treatments. There were no significant differences among treatments in total leaching losses of C, N, and base cations. Our findings suggest that enrichment of biochar with dairy manure effluent can promote C and N storage in soil and provide additional environmental benefits.

Fluorescence microscopy techniques for quantitative evaluation of organic biocide distribution in antifouling paint coatings: application to model antifouling coatings

A test matrix of antifouling (AF) coatings including pMMA, an erodible binder and a novel trityl copolymer incorporating Cu2O and a furan derivative (FD) natural product, were subjected to pontoon immersion and accelerated rotor tests. Fluorescence and optical microscopy techniques were applied to these coatings for quantification of organic biocide and pigment distribution. Total leaching of the biocide from the novel copolymer binder was observed within 6 months of rotor immersion, compared to 35% from the pMMA coating. In pontoon immersions, 61% of the additive was lost from the pMMA coating, and 53% from the erodible binder. Profiles of FD content in the binders revealed an accelerated loss of additive from the surface of the CDP resulting from rosin degradation, compared to even depletion from pMMA. In all samples, release of the biocide was inhibited beyond the Cu2O front, corresponding to the leached layer in samples where Cu2O release occurred.

Effects of sintering atmosphere on cement clinkers produced from chromium-bearing sludge

The purpose of this study was to investigate the effects of sintering atmosphere (oxidizing and reducing) on the polymorphs of dicalcium silicates (Ca2SiO4, C2S) and on the chromium leaching of the belite-rich clinkers made from a chromium-bearing sludge. This sludge was generated in an electroplating factory, and in addition to chromium, it contained nickel, copper, and zinc. In the clinker production, air was used as the oxidizing atmosphere, and carbon monoxide, which was produced by burning graphite with an insufficient amount of oxygen, was employed as the reducing atmosphere. Dicalcium silicates were substantially formed under both kinds of sintering atmosphere, but there was some nonhydraulic γ-C2S in the clinkers produced under the oxidizing atmosphere. In addition, the amount of γ-C2S decreased with the chromium-bearing sludge addition, whereas that of β-C2S increased. The clinkers produced under the reducing atmosphere had less residual chromium, a finding that shows that more chromium was evaporated. However, the reducing atmosphere can decrease the proportion of hexavalent chromium (Cr(VI)) in the resulting clinkers. For other heavy metals, the residual amounts of nickel and copper generally increased with the sludge addition, but zinc was absent in most of the clinkers produced under the reducing atmosphere. This implies that the evaporation of zinc is much more significant than that of the other heavy metals under a reducing atmosphere. In the leaching tests, the concentrations of nickel, copper, and zinc were below the detection limits in all the leachates. In terms of chromium, the total leaching concentration was highly related to Cr(VI). The clinkers produced under the oxidizing atmosphere had high leaching concentrations of chromium, and thus failed to meet the regulatory limit. In contrast, the reducing atmosphere was effective in decreasing the chromium leaching, and it therefore makes the resulting cement clinkers more environmentally sound. Implications: This study presents the effects of oxidizing/reducing atmosphere on the polymorphs of C2S and on the oxidation states of chromium in the clinkers. The chromium-bearing sludge from an electroplating factory was employed as a cement raw material. The reducing atmosphere was used to prevent the chromium from oxidizing to Cr(VI) during the sintering process, thus decreasing the chromium leaching concentrations of the resulting clinkers.

Leaching evaluation of cement stabilisation / solidification treated kaolin clay

Sustainable land management often requires redevelopment of existing and often contaminated Brownfield sites over use of Greenfield or agricultural land. Stabilisation / solidification (S/S) offer a viable remediation option with particular suitability in treating heavy metal contaminants. However, uncertainties over long-term durability and previously cheap landfill disposal costs resulted in limited use in many countries. There is a need to characterise treated material and assess components containment and release, to improve S/S confidence and inform remedial design, using the evaluation of the leaching controlling mechanisms. To improve understanding of key features that will enable improvements to such designs, this paper presents an evaluation of leaching for CEM II stabilised kaolin, using the leaching behaviour of 4 main components—aluminium, silicon, calcium and sulphur. Results show no detrimental implications on chemical durability due to kaolin degradation with hydration under induced alkalinity, with increased formation of stable cementitious minerals. Availabilities for components show that aluminium and silicon had minimal leachability compared to total content, whilst calcium and sulphur show almost total leaching availability. Decreasing calcium and silicon leachability under natural chemical conditions with increased hydration duration supports the increased formation of stable cementitious products with time, using the products of kaolin dissociation.

Leaching characteristics of bromine in coal

Comparative column leaching experiments were carried out on coal samples collected from Moxinpo Mine in Chongqing, Southwest China. Different acid solutions were used to investigate the leaching behavior and potential environmental effects of bromine in coal. The leaching rate and maximum leached concentration of bromine were calculated on the basis of the concentration of bromine in different resulting leachates measured by inductively coupled plasma mass spectrometry. The results show that the modes of occurrence and locations of bromine in coal, time, and pH value play an important role in controlling the leaching behavior of bromine in coal. At 120 h, the maximum leached concentration and the total leaching rate of bromine in coal increased with an increase in the acidity of the leaching solution. The amount of bromine released from coal leached at a pH of 2 accounted for 80.65% of its total leached amount for 40 h, whereas it was 89.42% at a pH of 4 for 50 h. When leached by an acidic solution, the bromine present in carbonate and Fe–Mn oxides located on the surface of coal particles may be released first, followed by the bromine in water-soluble and exchangeable forms in the interior of the coal matrix. The experiment showed that the bromine in coal may be leached out by acidic rain and enters the surrounding soil and surface water, resulting in the enrichment of bromine in the environment.

The Effect of Fly Ash on Calcium Leaching Properties of Cement Pastes in Ammonium Chloride Solution

The damage process of pure cement pastes with water to cementing material ratios of 0.30, 0.40, 0.50 and 0.60 and fly ash modified pastes with mass fraction of 10%, 30%, 40% and 55% were studied by using ammonium chloride solution with concentrations of 6 mol/l. The total leaching depth, leaching depth, porosity and compressive strength of these pastes leached for 14, 28, 56, 91 and 140 days were tested. The influences of W/C ratio and fly ash content on these properties were analyzed, the relationship between the two factors and the corrosion resistance of pastes was summarized. The results show that the total leaching depth of fly ash modified paste is larger than that of pure cement paste. However, the fly ash modified paste suffers various degree of lowered increment in porosity and strength loss (in percentage) in connection with the added content.

Effect of crystallization on the hydrolytic stability of basalt-like matrices with actinides

The effect of crystallization induced by self-α-irradiation on the leaching with water of basalt-like matrices with the incorporated α-emitting radioactive waste components was studied. Both the total leaching and the leaching of particular radionuclides (Pu and Am) were studied. Although radiation-induced crystallization leads to a certain increase in the leach rate, the effect is observed within a short period. Generally the crystallization of boron-containing basalt-like systems does not significantly impair their hydrolytic stability.

A new process of extracting vanadium from stone coal

A new process of extracting vanadium from the stone coal vanadium ore in Fangshankou, Dunhuang area of Gansu Province, China was introduced. Various leaching experiments were carried out, and the results show that the vanadium ore in Fangshankou is difficult to process due to its high consumption of acid and the high leaching rate of impurities. However, the leaching rate can be up to 80% and the content of V2O5 in the residue can be between 0.22%–0.25% in the process of ore fine grinding→oxidation roasting→mixing and ripening→aqueous leaching→P2O4 solvent extraction→sulfuric acid stripping→oxidation and precipitation→decomposition by heat. Also, the quality of flaky V2O5 produced by this process can meet the requirements of GB3283–87. The total leaching rate of vanadium is 70%. Also, three types of wastes are easy to treat. The vanadium extraction process is better in relation to the aspect of environmental protection than the sodium method.