جستجوی مقالات مرتبط با کلیدواژه "رهاسازی" در نشریات گروه "آب و خاک"

To investigate the release of nitrogen. Phosphorus and potassium elements from biochar, an experiment was conducted in a completely randomized design in three replications. Biochars were used by 2% in weight (W/W). The experimental treatments included control soil (CS), Soil+ Grape waste biochar (GSB), Soil + wheat straw and stubble (WSB) + brown walnut shell biochar (NSB) and Soil. The samples were incubated for about four months and sampling was done at days of 0, 7, 14, 28, 42, 56, 88 and 120. The results showed that the biochar addition significantly increased the concentrations of nitrogen, phosphorus and potassium in all biochar-amended soils compared to the control soil. Nitrogen concentration ranged from 766.6 mg kg-1 in control (average of sampling times) to 1272.2, 1366.7, and 1488.9 mg kg-1 in GSB, WSB and NSB treatments, respectively. Phosphorus concentration enhanced from 44.5 mg kg-1 in control (time-average of sampling) to 79.1, 67.1, and 70.8 mg kg-1 in GSB, WSB and NSB, respectively, and the concentration of potassium in the control increased from 103 mg kg-1 to 656.5, 293.8, and 125.6 mg kg-1 in the GSB, WSB, and NSB treatments, respectively. The WSB and NSB treatments released an average of 52% and 50.5% of their nitrogen content, respectively during 120 days, increased while GSB released only 28.6% of its total nitrogen on average. The order of nitrogen release rates in biochar were as follows: WSB≥ NSB> GSB. Regarding the release of phosphorus, NSB was considered to be the most efficient biochar, which was able to release 5% of its phosphorus during 4 months, while, GSB was the lowest effective biochar releasing only 0.5% of its phosphorus during the corresponding time. The order of phosphorus release from biochar treatments was as follows: NSB > WSB > GSB. The amount of available potassium in GSB was 2.3 to 6.7 times higher than the other treatments. The order of potassium release from biochar treatments was as follows: GSB > WSB > NSB. The results of infrared spectroscopy showed that the dissolution of amides containing nitrogen is the main mechanism of N release. The decrease in pH caused by nitrification, probably facilitated Ca-P dissolution from biochar and led to a higher phosphorus release.

Zn-Pb mine tailings of Zanjan (province of Iran) contain high concentrations of toxic metals, especially arsenic that can potentially release into the surrounding soils and water pathways. These tailings create leachate due to their connection with water, which is very dangerous to the environment and to the masses of animals and human beings. Unfortunately the geochemical and mineralogical processes that control arsenic release from tailings are not fully studded. Therefore this research aimed to assess the leaching characteristics of arsenic under different environmental conditions to recognize the parameters and factors controlling its concentration in the leachate.

Leaching of arsenic from Zn-Pb mine tailing was investigated in various environmental scenarios. In order to determine the amount of leached arsenic in different conditions, four leaching protocols, including toxicity leaching procedure test (TCLP), synthetic precipitation leaching procedure test (SPLP), field leach test (FLT) and leachate extraction procedure (LEP) were used. Also, to study the effect of various factors such as pH, contact time, particle size and solid to liquid ratio on leaching of arsenic from Zn-Pb mine tailings batch leaching experiments were carried out. Risk assessment code (RAC) based on fractionation method was also applied to evaluate the environmental risk of arsenic mobility.

The results indicated that in both samples of tailings ,the highest amount of arsenic was measured in the residual fraction that is relatively stable under natural environmental situations. According to RAC index, the tailings in term of arsenic placed in the low-risk tailings group. In TCLP, LEP, FLT and LEP test the concentrations of leached arsenic were low and the highest leaching concentration of arsenic occurred in the LEP test and sample S1. According to SPLP analysis, Zn-Pb tailings will have a high potential for contamination of surface and underground water. The mobility of arsenic in the tailings was entirely influenced by pH, contact time, particle size and solid to liquid ratio. The leaching of arsenic enhanced in acidic and alkaline condition and the amount of arsenic leached in acidic condition was much higher than that leached in alkaline condition. In fact, pH-dependent leaching behavior of arsenic from Zn-Pb mine tailing was amphoteric. Actually pH-dependent leaching behavior of arsenic from Zn-Pb mine tailings was amphoteric. In sample S1, the highest amount of arsenic was released from particles with the size of 500-600 µm, while in the sample S2 particles with the size of 150-250µm released the highest amount of arsenic.

By considering the results of leaching protocols, and arsenic fractionation and also with regards to factors affecting the concentration of arsenic in leaching water, reducing the pore water and contact time, and controlling the pH and preventing the spreading of tailings in the environment are the most important factors in preventing and managing the spread of pollution in the environment.

Cupper (Cu) is one of the micronutrients and the release rate of this element is an important factor in determining its bioavailability in calcareous soils. In this research, the kinetics of native Cu extraction by DTPA was studied in 21 calcareous surface soils (0-30 cm) and the best kinetics model to describe the data was selected. For this purpose 20 mL of 0.005 M DTPA solution was added to 10 g air dried soil and shacked,then during the 0.16 to 200 hours the concentration of Cu was determined. Furthermore the abilities of  zero, first, second and third order equations, simple Elovich, two constant rate, parabolic diffusion, Lagergern first order and Blanchard equations in description of the kinetics process were evaluated. According to the results, the rate of Cu extraction by DTPA was increased with time then reached a relative equilibrium in 72 hours. The best models for describing kinetics of Cu extraction during 200 hours were the simple Elovich and two constant rates. Also within 0.16 to 20 hours besides these two equations, the parabolic diffusion was one of the best models, too. Lagergern first order and Blunchard equation despite the wide range of correlation coefficients did not have a good fitness with the 21 studied soils. The αsβst product of simple Elovich equation (qt = 1/βs ln(αsβs) + 1/βs lnt ( in initial 15 minutes was larger than 1 for all studied soils. The amounts of constant b in the constant rate equation (qt = atb) were positively and negatively correlated with sand concentration (r= 0.47 *) and CEC values (r=-0.45*), respectively. The highest correlation coefficientsbetween the kinetics parameters of superior equation, was observed between the ab with βs.

The efficiency of singular and joint usage of third larval instars of ladybeetle, Hippodamia variegata</em> (Goeze) and green lacewing, Chrysoperla carnea</em> (Steph.) was studied against cotton aphid, Aphis gossypii</em> Glover on cucumber plants in greenhouse. The predator-prey ratio of 1:30 reduced the population of pest significantly. Singular and joint usage of predators, however, was not significantly different. The predator-prey ratio of 1:90 reduced the population of host significantly but the treatment with larvae of both predators and the treatment with only ladybeetle larvae were not significantly different. However, only the treatment with lacewing larvae was significantly different from the two above-mentioned treatments.