Ammonium Acetate Method Research Articles

Need to revisit potassium soil test methods: ammonium acetate method does not correlate with tuber yield and potassium uptake in potato

The study was driven by concerns regarding lack of response to K applied as per existing soil test based fertilizer recommendations in case of the potato crop in northwest India. Geo-tagged surface soil (0-15 cm) samples 180 were collected from three (60 each) different fields (named A, B and C) followed by pot experiment involving potato planted to 30 different surface (0-15 cm) soils using two K levels (0 and 60 kg K2O ha−1). Cate-Nelson (CN) model, and non-linear segmented linear-plateau (LP) and quadratic-plateau (QP) models were used to compute critical K levels by relating relative yield with soil test K using five different methods: 1 M ammonium acetate (AA K), ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA), Mehlich-3, sodium tetraphenylboron (STPB) and 1 M boiling nitric acid. These were validated by conducting fertilizer response trials (six K fertilizer levels- 0, 15, 30, 45, 60 and 90 kg K2O ha−1) at four sites. AA K correlated with other soil K extractants in the order: AB-DTPA (r = 0.93**, 0.27* and 0.67**)> STPB K (r = 0.71**, 0.27* and 0.39**) whereas AA K generally did not show any correlation with HNO3 K. AAK method was poorly correlated with yield and plant K uptake (r = 0.15, 0.24, respectively) in comparison to AB-DTPA (r = 0.75**, 0.64**), Mehlich-3 (r = 0.78**, 0.72**), STPB (0.58**, 0.76**) and nitric acid method (0.55**, 0.44*). Thus, multi-nutrient extractants like AB-DTPA and Mehlich-3 are better (than AAK) indices of plant available K.

Optimization of calcium carbide residue utilization for producing high‐quality calcium carbonate

AbstractIn light of the current situation where the utilization of calcium carbide slag yields low profits but holds significant potential for reducing carbon emissions, ammonium acetate was employed to leach calcium carbide slag. It also played a crucial role in regulating the products of indirect carbon dioxide carbonation when mixed with glycine and lye. Ammonium acetate's significance underscores its dual role in both the leaching and carbonation processes. This process yielded calcium carbonate with particle sizes smaller than 100 nm, with a purity of 98% and a single vaterite phase. The calcium carbide residue demonstrated an impressive CO2 uptake rate of 23.5%. Ammonium acetate exhibited an efficiency of 79.2% as a leaching agent. The ammonium acetate method demonstrated enhanced environmental friendliness and facilitated a more efficient carbon uptake rate of 23.5% compared to conventional indirect methods. Furthermore, the addition of lye, glycine, and ammonium acetate effectively extended the nucleation time of the calcium carbonate crystals and induced the formation of more vaterite intermediates with smaller particle sizes. The influence mechanism of compound additives on the carbonation reaction was revealed through kinetic analysis and molecular dynamics. This innovative approach offers a promising avenue for simultaneously treating solid waste and reducing CO2 emission. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Comparison of Soil pH and Exchangeable Cation Quantification by Various Wet Methods with Near- and Mid-Infrared Spectroscopy Prediction

ABSTRACT Rapid soil analyses can be obtained by infrared (IR) spectroscopy, but few studies have evaluated the suitability of different reference wet chemical methods to calibrate models predicting soil fertility. The aim of this study was to assess the accuracy of IR spectral-based models for the determination of soil pH measured in water, potassium chloride (KCl), and calcium chloride (CaCl2), and exchangeable basic cation content measured by the ammonium acetate (NH4OAc, 1 M and 0.02 M variations, pH = 7), Mehlich-III, Ambic-I, citric acid (1%), compulsive exchange, and Bray-II methods. Near- to mid-infrared (NIR, MIR) spectral-based models predicting soil pH and exchangeable cations measures were calibrated by partial least squares regression for a set of soils containing highly and intermediately weathered clay minerals and variable sesquioxide contents. The ratio of root mean square error of prediction (RMESP) to analyte component range was compared to a threshold value for contextual model accuracy assessment. pH measurements in CaCl2 matrices led to better calibrations and predictions of soil pH by IR spectral models compared to pH measurements in water and KCl matrices. Exchangeable calcium (Ca) and magnesium (Mg) concentrations determined by compulsive exchange and the NH4OAc (1 M, pH = 7) extraction methods, respectively, were most accurately predicted by NIR spectral-based models (RMSEP = 1.2–1.4 and 0.37 cmolc kg−1, respectively). The ratio of performance to inter-quartile distance (RPIQ) is recommended as an alternative figure of merit to traditionally reported ratio of performance to deviation (RPD) for IR spectral-based models predicting soil chemical properties. Subsetting soil samples by similarities in physiochemical properties improved the accuracy of soil pH and exchangeable Ca content predictions.

Cytochrome oxidase I (COI) revealed differentiation among populations of Atule mate in the coastal waters of Persian Gulf and Sea of Oman (Bushehr, Bandar Abbas, Chabahar)

This study investigated the genetic structure of the yellowtail scad (Atule mate) population based on the mitochondrial cytochrome oxidase subunit I gene sequences by collecting 90 specimens of Atule mate from Bushehr, Bandar Abbas and Chabahar in Iran. Mitochondrial DNA was extracted using ammonium acetate method. The PCR reaction was performed using a primer pair of the nucleotide sequences of the mitochondrial COI gene and its PCR products were sequenced. Out of the 13 haplotypes identified through evaluating the sequences, one haplotype was common within the sampling areas. The mean haplotype diversity was high (0.762±0.044) and the mean nucleotide diversity was low (0.003±0.0003). The longest genetic distance of 0.243 (P<0.05) was observed between the samples collected from Chabahar and Bushehr and the lowest of −0.048 (P>0.05) between the samples collected from Bandar Abbas and Bushehr. The mean values of Tajima’s D and Fu’s Fs were respectively calculated as −0.232 and 0.485 (P>0.05). Analysis of molecular variance (AMOVA) showed a high intra-population genetic diversity and a low inter-population diversity, which suggested a high gene flow among the study areas. The present findings suggested, probably the population of yellowtail scad in Chabahar constitutes a independent gene pool of other regions, and despite the unity of the populations of Bandar Abbas and Bushehr, their molecular diversity is acceptable. These results can help genetically manage Atule mate populations in the study areas and manage stocks and monitor genetic variations in this species.

A Study the Relationship of Soil Quality with Land Suitability for Coconut (Cocos nucifera L.) Development in Kebonagung Sub-district, Pacitan District

This study aims to assess the soil quality index (SQI) under the shade of coconut (Cocos nucifera L.) and its relationship to land suitability to provide recommendations for improvement to increase coconut productivity. This research conducted in Kebonagung District, Pacitan District using descriptive survey method. Land Map Units (LMU) are determined by overlaying soil type, land use, slope, and rainfall maps. Determination of survey using purposive sampling with 10 sample and three replications. The samples were analyzed in the laboratory with analysis method Bulk Density (Pycnometer), Porosity (Sample ring), Textures (Pipet), pH (Electrometric), Available P (Olsen method), Available K (NH4Oac 1 N extraction), Kjeldahl (Total N), Base saturation (Ammonium acetate extraction), SOC (Walkey and Black), CEC (Ammonium acetate method). Soil quality assessment was carried out using Principal Component Analysis (PCA) to obtain Minimum Data Sets (MDS). Land suitability was evaluated through the matching method with the conditions for growing coconut plants. The analysis showed that the soil quality index had a significant positive correlation with land suitability (r=0.768, p=0.004). The limiting indicators based on the correlation test were BV, pH, available P, organic C, and CEC. Suggested improvement recommendations include applying land cover crops, dolomite, manure, and balanced P fertilization.

Evaluation of simple and multivariate linear regression models for exchangeable base cation conversion between seven measurement techniques on South African soils

Conversions of exchangeable base cation concentrations between different analytical methods are required for comparisons of soil test results with norm values developed using specific methods. Different methods vary in extraction efficiency due to underlying chemical mechanisms of cation exchange. There is a lack of knowledge pertaining to the combined effects of soil physicochemical properties on the accuracy and parsimony of conversion models. Thus, the aim of this study was to develop equations for conversion of exchangeable base cation (Ca, Mg, K and Na) concentrations between seven different methods of measurement for soils dominated by moderate-activity clays. Additional objectives included the discussion of chemical mechanisms influencing nutrient extraction efficiency, development of root mean square error (RMSE) thresholds for model selection, and evaluation of the effects of soil physicochemical properties on model performance. The ammonium acetate (1 M and 0.2 M, pH = 7), compulsive exchange, Ambic-I, Mehlich-III, Bray-II and Citric acid (1%) soil test methods were performed on 57 soils from a Mediterranean climatic zone. Simple linear regressions (SLR) as well as multivariate linear regressions (MLR) incorporating soil physicochemical properties as parameters were developed. The accuracy of cross-validated models was comparable to accuracy of predictions for samples included in calibration. MLR equations (RMSECV = 1.4–1.6 cmolc kg−1, 0.4 cmolc kg−1, 16–20 mg kg−1 and 25–40 mg kg−1 for Ca, Mg, Na and K, respectively) were generally more accurate than SLR models. Relationships between Ca content extracted by different methods depended on soil alkalinity. Use of the developed SLR or MLR models to convert nutrient quantities between different methods should be chosen based on contextual accuracy requirements.

Molecular Identification of Captive Snakes from their Shed Skin Using Cyt b &amp; 12s rRNA Markers

Aims: To successfully utilize non-invasive shed skin samples for species identification of captive snake species of Tamil Nadu and create genetic repository.&#x0D; Study Design: The experiment was designed to apply the ammonium acetate method of DNA extraction from shed skin. Two mitochondrial markers were used to ascertain identification of species.&#x0D; Place and Duration of Study: Advanced Institute for Wildlife Conservation (AIWC), Tamil Nadu Forest Department, Vandalur, Chennai, Tamil Nadu. The samples were collected between May and October 2019 from Arignar Anna Zoological Park, Vandalur, Guindy National Park, Chennai, and Amirthi Zoological Park, Vellore, Tamil Nadu.&#x0D; Methodology: We collected fresh shed skin from 8 different snake species from captivities of zoos and dried between 48 to 72 hours to remove moisture. Independent DNA isolations were performed for each sample. The DNA isolated samples were quantified using Nanodrop Spectrophotometer for concentration. Independent PCR amplification of mitochondrial regions of cytochrome b and 12S rRNA were performed and agarose gel electrophoresis was carried out. PCR products were subjected to sanger sequencing using genetic analyzer.&#x0D; Results: The DNA concentration from all 8 different snake species ranged between 250 to 1600 ng/µL and average quality ratios A260/280 of 1.85 and A260/230 of 2.10. Both the mitochondrial gene regions cytochrome b and 12S rRNA showed specificity in species amplification with NCBI BLAST result ranging from 99-100%. Phylogenetic trees using maximum-likelihood method classified closely related species under the same clade, with a bootstrap support of 60-100%. Genetic distances of snake species ranged from 0.148-0.457 in cytochrome b region and 0.148-0.457 in 12S region.&#x0D; Conclusion: Shed skin is often overlooked from utilization for species identification. In this study, DNA from shed skin of 8 captive snakes is extracted and amplified using Cyt b and 12s mitochondrial markers. Individual phylogenetic trees are constructed for each marker to find relatedness of different snake species with one another. This work is an initiation of genetic repository creation of captive snake species of Tamil Nadu and could be effectively employed in conservation and population genetic studies of snakes.

Extractable Potassium as Affected by Soil Moisture Conditions

ABSTRACT Soil potassium (K) analysis is a widely adopted tool to evaluate exchangeable K content, but variations in soil moisture before sampling, the drying method, and the extractant used could influence the results. Therefore, the objectives of this work were as follows: evaluate the effect of soil drying before testing on extractable K; evaluate the effect of a short-term flooding on soil K availability; and determine the relationships between field-moist and oven dried soil K concentrations extracted with Mehlich-3 and Ammonium Acetate (NH4OAc) methods, with and without recent K application. Five Uruguayan agricultural soils were incubated in pots at different humidity levels, and they were analyzed field moist (FM), air-dried (AD) and oven-dried (OD), using two different extractants: NH4OAc and Mehlich-3. The K concentration from FM sample were higher than from OD for both extractants, except for the soil with the lowest K value and the non-illitic clay mineral, where the results were opposed. The K concentrations from FM of samples with 100% humidity were higher than those of 50%. No significant effect on K availability was detected due to the occurrence of short-term flooding before sampling. NH4OAc extracted more K than Mehlich-3 in all soils and treatments.

Methylene Blue Spot Test for Cation Exchange Capacity (CEC) Estimation in Acid Soils of India

In order to establish a simple, rapid and cost effective method of estimating cation exchange capacity (CEC) of acidic soils, we tested the utility of methylene blue spot test (MBST) vis-à-vis commonly used neutral 1N ammonium acetate method (NAAM) in twenty acidic soils. The soils collected from ten different states of India varied widely in pH, organic carbon content and texture. Averaged across the soils, MBST-CEC was 37% lower than the NAAM-CEC, due possibly to the differences in pH at which the two methods operate. The CEC values estimated by MBST correlated strongly (R=0.89) with those obtained by NAAM, implying that MBST can be used satisfactorily to measure CEC of acidic soils. An equation for inter-conversion of CEC values obtained by the two methods was also worked out. Since NAAM is a time taking and tedious procedure, we recommend MBST method for routine estimation of CEC in acidic soils of India. The method is easily applicable with simple test equipments including filter papers, a glass rod or dropper and methylene blue dye. More than 60 samples a day can easily be analyzed for CEC using MBST method. Being a simple, rapid and cost effective method, the MBST can be included in rapid soil testing kits. Given the importance of CEC in soil fertility and plant nutrition, MBST-CEC may also be included in the soil health cards distributed to the farmers.

Characterization of Philippine natural bentonite

Abstract Philippine natural bentonite is characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM), chemical analysis, thermogravimetric-differential scanning calorimetry (TG-DSC), and Fourier transform infrared (FTIR) analysis. The cation exchange capacity (CEC) was also measured. XRD shows that the mineral is composed primarily of mordenite, hectorite, and montmorillonite. SEM shows the flaky and porous structure of the bentonite powder. Chemical analyses show that SiO2 (47.90 wt%) and Al2O3 (14.02 wt%) are the major components of the clay. TG-DSC shows that the mineral contains 15.55% moisture. IR transmittance spectrum shows the common vibration bands present in the sample which include O–H stretching of inter-porous water, symmetric and asymmetric stretching of hydroxyl functional groups, asymmetrical stretching of internal tetrahedra (O–Si–O and O–Al–O), symmetrical stretching of external linkages, and so on. The measured CEC were found to be 91.37 and 43.01 meq/100 g according to the ammonium acetate method and barium acetate method, respectively.

A simple silica based DNA isolation method for cell-free DNA analysis from liquid biopsy

Abstract Objectives Cell-free DNA (cfDNA) is a promising biomarker for cancer diagnostics. Blood is used as a liquid biopsy material which transports many types of biological components such as protein, circulating tumor cells, cfDNA, and extracellular RNA molecules. In this study, the yield and purity of extracted DNA were compared of seven different in-house DNA isolation methods and two different commercial kits from human blood samples. Methods Different in-house methods, guanidine thiocyanate (GuSCN) with silica method, phenol-chloroform-isoamylalcohol method-1, phenol-chloroform-isoamylalcohol method-2, phenol-chloroform-isoamylalcohol with ammonium acetate method, sodium N-lauryl sarcosine with glycogen method, sodium acetate method, sodium chloride with silica method and two different commercial kits “Quick-cfDNA serum &amp; plasma kit” and “plasma/serum cell-free circulating DNA purification mini kit” were used. After DNA isolation, methods were compared with real time PCR technique (qPCR) and spectrophotometric methods. Results The results showed that the newly modified GuSCN with silica method gave much higher purity and yield than any other analyzed in-house isolation methods and commercial kits that were used. Conclusions The GuSCN with silica method is simple to set up, easy to use, inexpensive and environmentally safe. The method would be an alternative method for cfDNA isolation from liquid biopsy samples.

Landscape and Soil Characteristics of LandslideAffected Cadac-an Watershed in Leyte, Philippines

The continuous and increasing degradation problem in Leyte watershed due to landslide occurrences explains the importance of the characterization of these areas. Hence, this study was carried out to characterize the landscape and soil properties in the landslide-prone watershed. Landslide cuts, serving as representative soil profiles in Cadac-an watershed, were used for examination and characterization. Among the landscape characteristics determined were fault line, geomorphology and land use. Profiles were sampled for the analyses of soil properties such pH (Potentiometric method), percent organic matter (OM) (loss of weight on ignition), available phosphorus (P) (Olsen extraction method), cation exchange capacity (CEC) (ammonium acetate method) and exchangeable bases: calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K). Cadac-an watershed was observed to be dominated by andesitic materials characterized by the presence of the active Leyte segment of the Philippine Fault. It is rugged and mountainous with brushes and grasses as the dominant vegetation. Generally, soils from the landslide areas in Cadac-an watershed had a very strongly acidic to moderately alkaline pH, high to low OM and P content, very high to low CEC, high to low exchangeable K, Ca and Mg, and low exchangeable Na.

A comparison of cation exchange capacity of organic soils determined by ammonium acetate solutions buffered at some pHs ranging between around field pH and 7.0

Cation exchange capacity (CEC) and exchangeable cations are among two of the most important measures for determining soil characteristics and soil quality. There are various methods of measuring CEC, including the ammonium acetate method of Schollenberger and Dreibelbis (1930) which is buffered at pH 7.0 and the barium chloride-triethanolamine method of Mehlich (1938) which is buffered at pH 8.2. These CEC measurements can result in values very different from the CEC of the soil at its field pH (effective CEC or CECe), especially in acidic soils, such as organic soils, with pH-dependent CEC. Therefore, the focus of this article is the comparison of CEC of organic soils obtained using the different pH level of the extraction solution. Five organic soil and two mineral soil samples were used in this experiment. The variables tested were CEC and exchangeable cations using ammonium acetate solutions buffered at several pHs; field pHs (acidic) of 3.8, 4.2, 4.8 and neutral (7.0). Each soil sample and pH level were replicated three times. The decomposition rate of the five organic soil samples was determined using the pyrophosphate color method, which proved to be sapric. The results indicated a positive relationship between pH and CEC value, the higher the pH buffer the much higher the CEC measured. There was a considerable difference of CEC values produced from the varying pHs of extraction solution. However, the pH of the extraction had no substantial effect on measured exchangeable cations.

Long-term influence of different production systems on potassium buffering capacity of Typic Ustochrept soil

Imbalanced application of nutrients in the intensively cropped areas results in deterioration of soil fertility. Application of recommended dose of potassium (K) is essential for improving the use efficiency of other nutrients. To assess the buffering capacity of soil, three composite soil samples were collected from the surface soil (0–30 cm) during 2015 from 3 production systems viz., organic, inorganic and integrated which was maintained from 2004 with basmati rice–wheat–Sesbania system under Network Project on Organic Farming at ICAR-Indian Institute of Farming Systems Research, Modipuram. Fractionation of potassium (K) was achieved by sequential extraction of soil samples with distilled water, ammonium acetate and nitric acid in the same order. The relationship between the adsorbed and equilibrium potassium concentration, quantity was determined by plotting Freundlich adsorption isotherms. This was used to determine the buffering capacity and the concentration levels of potassium adsorbed on un-specific sites in the soil. The suitability of the adsorption equation was determined by applying the least square regression analysis. The results revealed that available potassium in the soils ranged from 119.51 to 135.01 mg/kg with 126.02 ± 5.24 mg/kg as mean (ammonium acetate method) while water soluble and nitric acid extracted potassium ranged from 28.51 to 29.05 mg/kg and 2594.49 ± 19.33 mg/kg (mean) in various production systems. The mean free energy of replacement was found to be −1998.01 ± 28.38 cal/mol indicating that soils have comparatively higher potassium supply under organic system. The potassium buffering capacity of the soils was found to be 0.7462 ± 0.16 mg/kg, 0.6295 ± 0.20 mg/kg and 0.6774 ± 0.09 mg/kg in organic, integrated and inorganic systems, respectively. The amount of potassium adsorbed on un-specific sites of the organic, integrated and inorganic systems was found to be 7.4730 ± 1.81, 15.11 ± 2.40 and 11.6 89 ± 3.58 mg/kg, respectively. It can be concluded that long-term organic production system improves K+ buffering capacity of Typic Ustochrept soil as compare to the integrated as well as inorganic production systems.

A new experimental multi-physics method for quantifying cation exchange capacity of shaly-sand formations

In this paper, a new method is proposed to quantify cation exchange capacity (CEC) in rocks with complex mineralogy and in the presence of multiple types of clay minerals by integrating nitrogen adsorption-desorption, nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) measurements (including quantitative XRD). In the new method, a successive controlled nitrogen adsorption-desorption measurements as well as NMR measurements were performed on multiple samples from the same rock type. Then, an inversion algorithm was introduced to estimate surface area and volume of hydration water of each mineral, which were used as inputs to our recently-developed novel physics-based CEC estimation workflow. The CEC estimates obtained from the new method were compared against those from the ammonium acetate method and inductively coupled plasma mass spectrometry (ICP-MS) measurements in synthetic and actual powdered shaly sand rock samples. The results showed that the CEC estimates from the two methods were in good agreement, with less than 4 meq/100 g difference (i.e., average relative error of less than 23%). The experimental results demonstrated reliability of the proposed method for CEC quantification in clay-rich formations with complex lithology in the presence of multiple types of clay minerals.

Comparison of Cation Exchange Capacity Estimated from Vis–NIR Spectral Reflectance Data and a Pedotransfer Function

Core Ideas Conventional methods for measuring CEC are time consuming and costly. A Vis–NIRS model and pedotransfer function (PTF) were developed for CEC determination. The Vis–NIRS model estimated CEC accurately for different soil types. The Vis–NIRS CEC model performed better than the PTF based on clay and organic C contents. Knowledge of the cation exchange capacity (CEC) for soils or other porous media is very important for civil engineering and agricultural applications. However, the standard laboratory methods to measure CEC are costly and laborious. The aim of this research was to develop a visible–near‐infrared spectroscopy (Vis–NIRS, 400–2500 nm) calibration model to predict CEC based on multivariate analysis and to compare the predictive ability of Vis–NIRS with that of a pedotransfer function (PTF). For this purpose, reference CEC was measured by the ammonium acetate method for 235 soil samples, collected from 21 countries. Diffuse spectral reflectance data were also collected by using a NIRSTM DS2500 spectrometer. The model was constructed on a calibration subset (80%) and evaluated with a validation subset (20%) using partial least squares regression. The Vis–NIRS calibration model was sufficiently robust based on the cross‐validation results [R2 = 0.79, RMSE of cross‐validation values of 7.9 cmolc kg−1 and bias = −0.14]. The independent validation of the Vis–NIRS model showed good prediction accuracy, regardless of sample origin (RMSE of prediction value of 5.0 cmolc kg−1 and ratio of performance to interquartile distance value of 4.5). Moreover, the Vis–NIRS prediction performance was superior to that of the PTF, which was influenced by the sample origin (RMSE values of 11.5 cmolc kg−1). The better prediction of CEC by the Vis–NIRS calibration model suggests that it is due to the co‐variation of CEC with clay (type and content) and organic C content.

Application of Modified Bentonites for Arsenite (III) Removal from Drinking Water

Four modified bentonites (La(III), Ce(III), Y(III), Fe(III)) were prepared by ion exchange process to remove arsenite (III) ions from water. The modified bentonites were examined with X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD). The rare earth (REE) and Fe(III) ion content in bentonite was higher than the CEC values obtained by ammonium acetate method related to trivalent ions (2.7 x 10-4 mol g-1). The kinetics, equilibrium time, sorption isotherms and desorption experiments were examined. Lanthanum, yttrium and cerium bentonite can bind similar amount of arsenite(III) ions. Iron-bentonite cannot bind significant amounts of arsenite ions. The active sites and the solubilities of the sorption complex were determined. Arsenite (III) ions sorb in the interlayer space as REEAsO3. The solubility of the arsenite complex was two orders of magnitude smaller than that of the phosphate complex. After desorption the eluted amount of arsenite (III) was 55 % related to the sorbed amount of arsenite. The d(001) basal spacing of modified bentonites and that of after sorption and desorption was measured. After the sorption of arsenite ion on lanthanum bentonite, the d(001) basal spacing of montmorillonite was decreased and after desorption an increase in d(001) basal spacing was observed again. Modified bentonites can be used for removing arsenic ions from water.

Cation exchange capacity of biochar: An urgent method modification

Biochar, produced through pyrolysis of organic matter, is negatively charged, thus contributing to electrostatic adsorption of cations. However, due to its porous structure and contents of alkaline ashes, the determination of the cation exchange capacity (CEC) is challenging. Literature values for the CEC of biochar are surprisingly variable and are often poorly reproducible, suggesting methodological problems. Here, we modify and critically assess different steps in the existing ammonium acetate (NH4OAc) method (pH 7), where ammonium (NH4+) is displaced by potassium chloride (KCl), following removal of excess NH4OAc with isopropanol, in batch mode. We used pigeon pea biochar to develop the method and conducted a test on three additional biochars with different acid neutralizing capacity. A pretreatment step of biochar was introduced, using diluted hydrochloric acid, to decrease biochar pH to near neutral, so that 1 M NH4OAc effectively buffers the biochar suspension pH at 7. This allows the CEC of all biochars to be determined at pH 7, which is crucial for biochar comparison. The dissolution of ashes may cause relatively large weight losses (e.g. for cacao shell biochar), which need to be accounted for when computing the CEC of raw biochar. The sum of NH4OAC-extractable base cations provided a smaller and better estimate of the CEC than KCl-extractable NH4+. We hypothesize that the overestimation of the CEC based on KCl-extractable NH4+ is due to the ineffectiveness of the relatively large isopropanol molecules to remove excess NH4OAc in biochars rich in micro-pores, due to size exclusion. The amount of base cations removed in the pretreatment was about three (rice husk biochar) to ten times (pigeon pea biochar) greater than the amount of exchangeable cations. The CEC values of biochar increased from 10.8 cmol/Kg carbon to 119.6 cmol/Kg carbon. These values are smaller than reported CEC values of soil organic carbon.

A new method for quantifying cation exchange capacity in clay minerals

Abstract In this paper, a new method is proposed to theoretically quantify cation exchange capacity (CEC) of pure clay minerals, by use of nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and nitrogen adsorption-desorption isotherm analysis. A theoretical model is introduced to estimate CEC, which is derived based on energy balance between chemical potential and electric potential energy. The change in chemical potential is a function of relative humidity and volume of hydration water. The change in electric potential energy is a function of the CEC, basal spacing, and surface area of clay minerals. XRD measurements were performed on clay minerals before and after exposure to 95% relative humidity. These measurements were used to estimate the basal spacing before and after hydration as well as the number of interlayers in each particle of clay minerals. NMR laboratory measurements were performed on the clay mineral samples before and after hydration to obtain the volume of hydration water. The nitrogen adsorption-desorption isotherms provided the surface area of clay minerals. The estimates of CEC from the new method were cross-validated against the directly-measured CEC, obtained from ammonium acetate method by use of inductively coupled plasma mass spectrometry (ICP-MS) measurements. The introduced method was successfully tested on six types of clay minerals (i.e., illite, kaolinite, chlorite, and three types of montmorillonite). The calculated CEC results from the new method were in agreement with those from the wet chemistry method, with less than 7 meq/100 g difference for all types of clay minerals. The experimental results on the performance of the new method demonstrated reliability of this method for quantification of CEC. The outcomes of this paper can be potentially applied to variety of formations with measurable concentrations of clay minerals such as shaly sands and organic-rich mudrocks for reliable assessment of CEC.

Chemical extractants in the evaluation of available silicon in acid soils, neutral and alkaline

The available silicon content has generally been determined in acid soils, but neglected its quantification in other soils, to be able to make recommendations of this element according to its content for each soil. The objective of this research was to evaluate the available silicon in soils of the department of Cordoba, Colombia by means of different chemical extractors. Samples of acid, neutral and alkaline soils were collected at the depth of 20cm and sent to the Laboratory of Soils and Waters of the University of Cordoba to determine the available silicon content. The chemical extractors were 0.01mol L-1 calcium chloride, 0.5mol L-1 acetic acid, 38.5g L-1ammonium acetate, pH 4.0 buffer (HC2H3O2 + CH3COONa) and the method proposed by the authors, named barium chloride solution. For extraction, 5g of soil were weighed and 50mL of extractant was added and the mixture was stirred for 1h at 220rpm, filtered and left standing for 12h. The quantification was performed in a spectrophotometer at a wavelength of 66nm and the chemical determination was performed in series with three replicates, analyzed by correlation and contrasts. In general, according to results of higher to lower concentration, silicon was presented in the following sequence of extraction, alkaline soils> neutral> acids. By means of the Tukey test and contrasts it was concluded that the barium chloride solution could be used as alternative to the reference method in the determination of silicon in the three types of soils. In addition, for alkaline soils, the ammonium acetate method 38.5g L-1 can also be used as an alternative for the determination of silicon.