Mirian Chieko Shinzato

Remoção de metais pesados em solução por zeólitas naturais: revisão crítica

Recent work on the application of natural zeolites to the removal of heavy metals in solution is discussed. Ionic selectivity sequences of natural zeolites, as well as parameters associated with their efficiency of adsorption and ionic exchange, are closely related to their crystal structure and the chemical characteristics of the ions in solution. It is noteworthy that some external variables such as temperature, pH and initial ion concentration can interfere in the process of removal of heavy metals in solution, as well as in the sequence of ionic selectivity. In general, ions with low energy of hydration have greater preference for available charged exchange sites within the zeolite framework. The efficiency of removal of ions with higher energy of hydration, in turn, can be controlled by its solution concentration: the less concentrated the better. It is evident, therefore, that natural zeolites have a great potential in the treatment of effluents contaminated by heavy metals.

Remoção de Pb2+ e Cr3+ em solução por zeólitas naturais associadas a rochas eruptivas da formação serra geral, bacia sedimentar do Paraná

The capacity of natural zeolites and its host rock (dacite) to remove Pb2+ and Cr3+ from aqueous solutions has been investigated. Results showed that both samples prefer to remove Pb2+ instead of Cr3+. Almost 100% of Pb2+ was removed from solutions with concentration until 50 mg L-1 and 100 mg L-1 of this metal, respectively by dacite and zeolite. The equilibrium of metals adsorption process was reached during the first 30 min by both materials. Na+ can be used to recover Pb2+, but not to remove Cr3+ from the treated samples. The Sips model showed a good fit for experimental data of this study.

Effect of disposal of aluminum recycling waste in soil and water bodies

This study evaluated environmental contamination by disposal of waste from tertiary aluminum industry in soil and water bodies. The main wastes of this industry are dross, non-metallic waste (product of dross leached with water) and liquid effluent. The water at the bottom of the pond, where the alkaline and saline aluminum effluent is discharged, presented high values of pH (>9) and high concentration of ammonia (N-NH3). However, dross disposal in soil decreased pH (<4) of groundwater and increased concentrations of Al3+, Na+, K+, Ba2+, Ni2+, Pb2+, Cu2+ and Zn2+. The N-NH3 produced from the reaction with water and some components of dross (aluminum nitride) probably promoted the increase of the nitrifying microbial activity in soil, which was responsible for the decrease in pH. In this condition, many components of dross were also easily leached into groundwater. The disposal of non-metallic waste into soil did not change the groundwater pH, but increased concentrations of Mn2+, Ba2+, Pb2+, Fe3+ and Ni2+. The disposal of aluminum recycling wastes without any treatment can change the quality of groundwater and surface waters, mainly due to high level of N-NH3, which modifies the pH of these waters and is very toxic to aquatic organisms.

Efeito da adição de zeólita e vermiculita na lixiviação de potássio do solo

This study aimed to investigate the leaching of potassium (K+) from the soil (Oxisol) and to evaluate the efficiency of uptake of this ion with the addition of minerals with high cation exchange capacity (CEC), such as vermiculite and zeolite. Oxisol samples collected in Araraquara (SP) were physically, chemically and mineralogically characterized. The leaching of potassium from the soil was performed using two tests: (1) K+ leaching using columns filled with soil, in the presence of vermiculite or zeolite, and (2) incubating soils with vermiculite and zeolite for 30 days to analyze the interaction between these minerals and the K+ added to the soil in the presence/ absence of Ca2+ (as CaCO3). The soil has clay texture and low acidity, and is poor in nutrients and mineral sources of K+. Tests in soil columns proved that the texture and mineralogy of the soil play an important role in the retention of K+, promoting its rapid transfer from the soluble to the exchangeable phase. The Oxisol released, on average, only 2% of the K+ added to the soil, and this value decreased to 1.6% in the presence of vermiculite and to 1.2% in the presence of zeolite. In the incubation test, it was also noted that the K+ added to the soil is rapidly transferred to the exchangeable phase, and that the retention rate of this cation increases in the soil in the presence of vermiculite and zeolite. However, the presence of calcium in the soil does not favor the retention of K+ by vermiculite - which retains preferably cations of higher valence, such as Ca2+. The same is not true for zeolite, since its exchange sites hold preferably lower valence cations, such as K+. In general, it was found that the addition of minerals with high CEC increases the amount of K+ in the fixed phase, which can serve as a reserve of this ion, and decreases the loss by leaching of this nutrient from the soil.

Anomalias de flúor nas águas subterrâneas do estado de São Paulo

This work examines the data compiled from the literature about the main occurrences of fluoride (F - ) in the groundwater of the State of Sao Paulo. The results of this study showed that at least 208 wells had high concentrations of F - (> 1.0 mg dm -3 ), 122 of which were considered anomalous (> 1.5 mg dm -3 ) and harmful when ingested in large quantities. Because of its high productivity and large-scale exploitation, the Guarani aquifer is the most studied one, but other aquifers, such as the Crystalline (Precambrian), Serra Geral and Tubarao aquifers, and the Passa Dois aquitard should also be considered important. In the past, the increase in the concentration of F - in the aquifers was related to hydrothermal processes and tectonic events with structural controls, such as the Gondwana supercontinent breakup, which would have enable the circulation of residual magma solutions, mineralization, and remobilization of the fluorine contained in the percolated rocks. Currently, the release of F - is caused due to the rock-water interaction under alkaline pH hydrochemical conditions, in typical sodium-bicarbonated (Na-HCO3) waters, poor in Ca 2+ , and under the influence of ionic strength, contact time, depth, temperature, ion exchange capacity, among others. In fissured aquifers of granitic composition and volcanic rocks, the minerals that can release F - into water are biotite and amphibole (where F - is replacing OH - , due to the similarity of its ionic radii) and, occasionally, secondary fluorite filling fractures and apatite. In sedimentary aquifers, F - is mainly found in clay minerals structures (illite, muscovite, smectite, vermiculite, kaolinite, among others) replacing OH - . Therefore, the high levels of F - in the groundwater are intrinsically associated with the characteristics and types of minerals of the aquifers.

ALTERAÇÃO EXPERIMENTAL DE ROCHAS CARBONÁTICAS, CAVERNA DAS PERÓLAS, IPORANGA (SP)

Experimental studies were performed to study the chemical weathering of carbonate rocks from the Perolas Cave, Iporanga municipality, State of Sao Paulo. Soxhlet extractors were used to accelerate the leaching process in two different ways: continuous and intermittent. The leaching solution obtained from the continuous test was chemically analyzed at the end of the process (about 454 hours), and the precipitates were separated and mineralogically analyzed by X-ray diffraction (XRD). In the intermittent leaching process, solutions and precipitates were collected after a predetermined period of time and chemically analysed to determine the number of ions removed from the weathered rocks. It was found that the ions mainly leached in the beginning of the experimental weathering were Na+ and Mg2+; however, when the leaching process was accelerated, Sr2+, Ba2+ and Ca2+ became the most remobilized ions, along with Na+, leading to the precipitation of calcite. In the continuous leaching test, it was observed that the concentrations of Sr2+ and Ba2+ were lower compared to the intermittent test, showing that these ions were probably co-precipitated with calcite. The low Mg/Ca ratio in the experimental leaching solutions may have caused the precipitation of calcite instead of aragonite. It was noted that there was a higher rate of remobilization of the constituents of the carbonate rocks on the level where the samples were subjected to fluctuations of the water table in the compartment of the Soxhlet equipment. Kaolinite is the main secondary mineral in the weathered rock.

Efeito da adição de lama vermelha nas propriedades eletroquímicas e de adsorção de um latossolo vermelho

This study aimed to characterize the waste generated in the production of alumina from bauxite refining process (red mud) and to analyze its effect on the electrochemical and adsorption properties of a tropical soil (Oxisol). The red mud (LM) is a highly alkaline residue (pH around 12), which is rich in iron oxide/hydroxides. To study the effect of red mud and calcium carbonate (CaCO3) - commonly used in agriculture to correct soil pH - on the soil, these substances were added in different proportions to Oxisol samples for 60 days. The addition of CaCO3 and LM to the soil increased the pH and the point of zero charge (PZC). However, the pH H 2 0 value of the soil with LM was greater than its PCZ, enabling dispersion of soil particles. Moreover, such addition increases cation exchange capacity in soils, as observed in removal tests of Pb 2+ in solution. It was observed that the minimal addition of 0.5% of CaCO3 and 10% of LM to the soil increased the Pb 2+ retention capacity from 37% to 100%. The same results were observed in tests performed only with red mud. Even when subjected to an acid leaching (solution with pH 4.9), soils incubated with 1% CaCO3 and 1% LM released 7.5% and 11% of retained Pb 2+ , respectively. This low Pb 2+ leaching rate is due to the increase in soil pH, favoring the adsorption of Pb 2+ by Fe and A1 oxy-hydroxides present in the soil and red mud composition. It can be concluded, therefore, that the addition of red mud can change the electrochemical conditions of the soil, dispersing more clay and colloidal particles. However, by increasing the pH of the system and introducing iron and aluminum oxides and hydroxides, such material can increase the retention of heavy metals, such as Pb 2+ , in the soil.