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Authors
Abstract(s)
O fósforo é um elemento-chave na vida, utilizado na reprodução e crescimento de
imensas espécies. É também utilizado extensivamente na indústria agrícola como
fertilizante; no entanto, esta sobreutilização levou à presença de níveis críticos de fósforo
em efluentes, que pode levar à eutrofização de aquíferos. Os compostos organofosforados
são também amplamente utilizados na indústria agrícola, maioritariamente como
herbicidas, contribuindo também em larga escala para a poluição. Existe também uma
escassez de fosforite, uma das principais fontes não renováveis de fósforo. Por isso, têm
sido utilizadas várias tecnologias emergentes para a remoção e subsequente recuperação
de fósforo a partir de efluentes. Uma dessas tecnologias é a degradação por via
eletroquímica.
Este estudo teve como objetivo a degradação de um composto organofosforado, e a
remoção e recuperação de compostos fosforados por oxidação eletroquímica, a partir de
uma solução de glifosato contendo 10 mg/L de fósforo, através da utilização de um ânodo
de BDD e um cátodo de aço inoxidável. Os ensaios conduzidos tiveram uma duração
variável (1 a 6 h) e foram controlados galvanostaticamente (0,05 A a 0,3 A) ou
potenciostaticamente (5,0 V). Foi adicionado à solução cloreto de cálcio, de maneira a
aumentar a condutividade da solução e fornecer cálcio à solução com vista à recuperação
de fósforo através da precipitação catódica de fosfato de cálcio. Foram efetuadas variadas
análises para monitorização da eficiência de degradação, como análise de carbono
orgânico total e azoto total, cromatografia iónica e determinação da concentração de
ortofosfatos e fósforo total por métodos espetrofotométricos de absorção no UV-Vis.
Verificou-se que nos ensaios que decorreram a intensidades de corrente mais elevadas
(0,3 A) houve uma recuperação mais eficaz de fósforo, produzindo-se maior quantidade
de precipitado de fosfato de cálcio no ensaio de 6 h de duração. No entanto, nas amostras
dos ensaios conduzidos potenciostaticamente (a 5,0 V) não foi detetada a presença de
fósforo total na solução, embora o rendimento na formação de precipitado tenha sido
baixo, provavelmente porque o fósforo está na forma de peroxidifosfato, não detetado
pelo método utilizado.
As análises ao carbono orgânico total e azoto total mostraram um decréscimo constante
destes parâmetros ao longo dos ensaios, com a maior redução a acontecer a 0,3 A e 6 h
para ambos.
A formação de iões fosfato e a degradação do fósforo orgânico foi claramente visível na
análise espetrofotométrica de absorção no UV-Vis. A cromatografia iónica revelou uma redução na concentração de iões cálcio e cloreto em
todos os ensaios, sendo o cloreto oxidado a clorato (ClO3
-
) e perclorato (ClO4
-
), visíveis
nos cromatogramas. A formação de perclorato foi mais evidente nos ensaios de 0,3 A,
com a maior quantidade a ser formada ao fim de 6 h de ensaio.
Phosphorus is a key component of life, used in the growth and reproduction of many species. It is also used extensively in agriculture and farming industries as a fertiliser; however, this overuse has led to critical levels of phosphorus in wastewater, which can lead to eutrophication of water bodies and other major consequences. In addition, major usage of organophosphorus compounds in agriculture, such as herbicides, is a highly contributing factor to the pollution of water bodies. There is also a worldwide shortage of phosphate rocks, one of the main sources of phosphorus. Therefore, several new technologies for the removal and subsequent recovery of phosphorus from wastewater have been studied. One of such technologies with major potential is the electrochemical degradation of phosphorus compounds. This study aimed at the removal and recovery of phosphoric compounds by anodic oxidation from a glyphosate solution containing 10 mg/L of phosphorus, using a BDD anode and a stainless-steel cathode. The conducted tests had a varying duration from 1 to 6 h and were either current-controlled (5 mA/cm2 to 30 mA/cm2) or potentialcontrolled (5.0 V). Calcium chloride was added to the solution as a way of increasing conductivity, as well as supplying the solution with calcium for possible precipitate formation. Several analytical methods were used for monitorization of degradation efficiency, such as total organic carbon and total nitrogen analysis, high-performance liquid chromatography, and UV-Vis absorption spectrophotometry. It was found that the tests conducted at high current (30 mA/cm2) were more efficient at recovering phosphorus (as calcium phosphate precipitates), with higher precipitate yields obtained at 6 h. However, the tests conducted at controlled potential (5.0 V) showed the highest removal of total phosphorus from the solution, but low precipitate yields, probably because phosphorous in solution was in a form not detected by the method utilized. Total organic carbon and total nitrogen analysis show a consistent decrease of total carbon and nitrogen throughout the tests, with higher reduction at 30 mA/cm2 and 6 h in both cases. The formation of phosphate ions and the degradation of organic phosphorus in the solution is clearly visible with UV-vis spectrophotometry. High-performance liquid chromatography data reveals a reduction in both chlorine and calcium across all tests, with the former being oxidized into chlorate (ClO3 - ) and perchlorate (ClO4-), visible on the chromatograms.
Phosphorus is a key component of life, used in the growth and reproduction of many species. It is also used extensively in agriculture and farming industries as a fertiliser; however, this overuse has led to critical levels of phosphorus in wastewater, which can lead to eutrophication of water bodies and other major consequences. In addition, major usage of organophosphorus compounds in agriculture, such as herbicides, is a highly contributing factor to the pollution of water bodies. There is also a worldwide shortage of phosphate rocks, one of the main sources of phosphorus. Therefore, several new technologies for the removal and subsequent recovery of phosphorus from wastewater have been studied. One of such technologies with major potential is the electrochemical degradation of phosphorus compounds. This study aimed at the removal and recovery of phosphoric compounds by anodic oxidation from a glyphosate solution containing 10 mg/L of phosphorus, using a BDD anode and a stainless-steel cathode. The conducted tests had a varying duration from 1 to 6 h and were either current-controlled (5 mA/cm2 to 30 mA/cm2) or potentialcontrolled (5.0 V). Calcium chloride was added to the solution as a way of increasing conductivity, as well as supplying the solution with calcium for possible precipitate formation. Several analytical methods were used for monitorization of degradation efficiency, such as total organic carbon and total nitrogen analysis, high-performance liquid chromatography, and UV-Vis absorption spectrophotometry. It was found that the tests conducted at high current (30 mA/cm2) were more efficient at recovering phosphorus (as calcium phosphate precipitates), with higher precipitate yields obtained at 6 h. However, the tests conducted at controlled potential (5.0 V) showed the highest removal of total phosphorus from the solution, but low precipitate yields, probably because phosphorous in solution was in a form not detected by the method utilized. Total organic carbon and total nitrogen analysis show a consistent decrease of total carbon and nitrogen throughout the tests, with higher reduction at 30 mA/cm2 and 6 h in both cases. The formation of phosphate ions and the degradation of organic phosphorus in the solution is clearly visible with UV-vis spectrophotometry. High-performance liquid chromatography data reveals a reduction in both chlorine and calcium across all tests, with the former being oxidized into chlorate (ClO3 - ) and perchlorate (ClO4-), visible on the chromatograms.
Description
Keywords
Bdd Fosfato de Cálcio Fósforo Glifosato Oxidação Eletroquímica