Natural Cation Exchanger Research Articles

Alterações nos atributos químicos de um latossolo pelo manejo de plantas invasoras em cafeeiros

O controle de plantas invasoras é uma das práticas de manejo mais intensivas na condução de lavouras cafeeiras, o qual provoca alterações nos atributos químicos do solo. Diante disso, os objetivos deste estudo foram: avaliar os efeitos dos diferentes sistemas de manejo de plantas invasoras em uma lavoura cafeeira nos atributos químicos de um Latossolo Vermelho distroférrico em relação ao solo sob mata nativa (MATA); e verificar a relação entre o teor de C orgânico do solo (COS) e a capacidade de troca de cátions efetiva (CTC a pH natural) e a capacidade de troca de cátions a pH 7 (CTC a pH 7). O estudo foi realizado na fazenda experimental da Empresa de Pesquisa Agropecuária de Minas Gerais (EPAMIG), localizada no município de São Sebastião do Paraíso, Minas Gerais. A área experimental foi plantada com cafeeiros da cultivar Paraíso, e o experimento foi instalado em blocos casualizados, com sete manejos de plantas invasoras e três repetições. Os manejos de plantas invasoras avaliados foram: sem capina (SCAP); capina manual (CAPM); herbicida de pós-emergência (HPOS); roçadora (ROÇA); enxada rotativa (ENRT); grade (GRAD); e herbicida de pré-emergência (HPRE). Cada manejo de plantas invasoras nas entrelinhas dos cafeeiros vem sendo realizado há 30 anos em três ruas, com 36 m de comprimento cada. As amostras de solo foram coletadas no centro das entrelinhas dos cafeeiros em dezembro de 2007, com cinco amostras simples por parcela, que perfizeram uma amostra composta em três profundidades (0-3, 10-13 e 25-28 cm). As seguintes análises químicas foram realizadas nas amostras de solo: pH em água, cátions trocáveis (Ca, Mg, K e Al), C orgânico (COS), capacidade de troca de cátions efetiva ou a pH natural (CTC efetiva) e capacidade de troca de cátions a pH 7. Os manejos apresentaram características contrastantes, variando desde métodos manuais até capinas químicas e mecânicas. Os resultados permitiram observar que a manutenção das plantas invasoras nas entrelinhas dos cafeeiros, adotada no manejo sem capina, contribuiu positivamente para as alterações dos atributos químicos (Ca trocável, CTC efetiva e CTC a pH 7,0) nas três profundidades estudadas; além disso, elevou o teor de C orgânico total na profundidade de 0-3 cm e pode contribuir para aumento e manutenção dos estoques de C em lavouras cafeeiras. Assim, o manejo SCAP nas entrelinhas dos cafeeiros pode ser adotado para a melhoria e manutenção dos atributos químicos em lavouras cafeeiras. Por outro lado, a utilização constante e por longo prazo (30 anos) do manejo HPRE reduziu os valores de pH nas profundidades de 10-13 e 25-28 cm e do Ca trocável, Mg trocável e CTC efetiva nas três profundidades estudadas, em relação aos demais manejos de plantas invasoras. Os valores de CTC efetiva do Latossolo Vermelho distroférrico apresentaram relação com o teor de C orgânico em 59, 60 e 47 % dos casos e de CTC a pH 7 em 65, 55 e 46 %, nas profundidades de 0-3, 10-13 e 25-28 cm.

Chabazite Biofilter for Enhanced Stormwater Nitrogen Removal

Enhanced nitrogen removal from stormwater using chabazite, a natural cation exchanger, was evaluated in a pilot-plant biofilter operated for 216 days. A parallel sand filter served as the control. The biofilters were subject to various operating modes including baseline periods of steady flowrate and loading, simulated high flowrate (storm) events following steady flowrates, high flowrates following extended no-flow periods, and with limited influent dissolved oxygen. Under steady-flow operation, chabazite removed 93% of ammonium and sand removed 87%; total inorganic nitrogen was reduced 35% by chabazite versus 15% by sand. In a simulated storm event following steady-flow operation, 97% of cumulative ammonia mass was retained by the chabazite biofilter versus 70% for sand. Following a 40 day no-flow period, the chabazite biofilter retained 98% of influent ammonium in a storm event while sand exhibited high effluent ammonium. Chabazite ammonium retention was high under limited influent dissolved oxygen, verses significant breakthrough by the sand biofilter. Chabazite media provided superior performance resiliency under dynamic conditions that typify stormwater treatment.

Fractionation of rare earth elements within bone mineral: A natural cation exchange system

The distribution of rare earth elements (REEs) within fossil bones is controlled by their partition coefficients between apatite and pore waters, and the rate of diffusion through the bone. Using simple theoretical models, we show that REEs are strongly fractionated from one another during diffusive transport and adsorption. Fractionation occurs due to the relative ease of substituting REE ions of differing ionic radius into the Ca sites in the apatite lattice, and the degree of fractionation is dependent on the rate of diffusion of ions within bone (and therefore the rate of recrystallisation). Variations in bone thickness, recrystallisation rate, and potentially pore water composition may all influence the relative distribution of REEs, and thus REE ratios within bones. Increases in bone thickness and reductions in either diffusion coefficients or the duration of REE uptake lead to enhanced fractionation of REEs in our model simulations. Interpretations of REE ratios in fossil bones either for palaeoenvironmental or taphonomic applications must consider how fractionation will influence REE ratios within bones, particularly when interpreting spatially resolved analyses within single bones.

Methods for reducing the ammonia in hybridoma cell cultures

The factors which limit the proliferation of eukaryotic cells in vitro are still not well known. Ammonia is believed to be toxic for mammalian cell proliferation and secretion. We have tried two approaches to reducing the ammonia in the medium. We first limited the ammonia produced by the cells by replacing glutamine by glutamate. Then, we used two chemical engineering methods to eliminate accumulated ammonia. In one the used medium was passed through a natural cation exchanger: the clinoptilolite. In the other, the culture medium was passed through a hydrophobic microporous hollow fiber module. Replacing the glutamine by glutamate reduced the medium ammonia concentration. The physicochemical removal of ammonia induced a better cell growth, but not a better specific antibody secretion.

Comparative characteristics of adsorption methods for obtaining crystalline insulin

Results of a comparative study of adsorptive procedures for producing crystalline insulin showed that porous sulfocation exchange resins have considerable advantages over cellulose derivatives, carboxylic or natural cation exchangers.

Cation-Exchange Equilibria in a Carboxylic Cation Exchanger and in Attapulgite Clay

Selectivity numbers for a synthetic cation exchanger of the carboxylic type (IRC-50) and the natural cation exchanger, attapulgite clay mineral, were determined for different pairs of cations. The results in IRC-50 for Na+-K+, Na+-Rb+, and Na+-Cs+ systems showed no marked selectivity. The resin phase was considered to act as a concentrated salt solution. Hence, differences in the selectivity numbers (K) were attributed to the differences in the activity coefficients in the concentrated resin-phase solution. In the alkaline-earth systems (Mg++-Ca++, Mg++-Sr++, and Mg++-Ba++) the resin showed more selectivity between its members than between those of the alkali series. The selectivity numbers were functions of the percentage of Mg in the resin. In the Mg++-Ca++ system, Mg++ appeared more strongly held at low percentages of Mg, whereas in the Mg++-Ba++ system, Ba++ appeared more strongly held at all percentages of Mg in the resin. These results were explained on the basis of formation of slightly dissociated complexes of the alkaline-earth metals with the carboxylic groups of the exchanger. The results in attapulgite clay for the Na+-K+, Na+-Rb+, and Na+-Cs+ systems showed marked selectivity. The selectivity numbers were functions of the percentage of Na in the clay. The differences in selectivity were greater in the Na+-Cs+ system than in the Na+-Rb+ system and, in the Na+-Rb+ system, greater than in the Na+-K+ system. The results were broadly understood on the basis of the bifunctional character of the clay. The differences in the selectivity numbers for the alkaline-earth metals in the clay (Mg, Ca, Sr, and Ba) are small as compared with those of the alkali metals. In general, the resin behaved as a moderately strong electrolyte with respect to the alkali metals. It behaved like a weak electrolyte with respect to the alkaline-earth metals. Attapulgite clay behaved like a weak electrolyte with respect to both the alkali metals and alkaline-earth metals. The results of the selectivitynumber curves for the clay resembled those of a bifunctional cation exchanger and a high cross-linkage resin.