Herbicides Mechanisms Involved in the Sorption Kinetic of Ionisable and Non Ionisable Herbicides: Impact of Physical/Chemical Properties of Soils and Experimental Conditions

Volcanic ash-derived soils (VADS, variable-charge soils) are predominant in some regions of the world, being of great importance in the agricultural economy of several emerging countries. Their amphoteric surface charge characteristics confer physical/chemical properties different to constant surface charge-soils, showing a particular behavior in relation to the herbicide adsorption kinetics. Volcanic soils represent an environmental substrate that may become polluted over time due to intensive agronomic uses. Solute transport models have contributed to a better understanding of herbicide behavior on variable- and constant-charge soils, being also necessary to evaluate the fate of herbicides and to prevent potential contamination of water resources. The following chapter is divided into four sections: physical/chemical properties of variable and constant-charge soils, kinetic adsorption models frequently used to obtain kinetic parameters of herbicides on soils, solute transport models to describe herbicide adsorption on VADS, and impact of experimental conditions of kinetic batch studies on solute transport mechanisms

Impact of Physical/Chemical Properties of Volcanic Ash-Derived Soils on Mechanisms Involved during Sorption of Ionisable and Non-Ionisable Herbicides

Volcanic ash-derived soils (VADSs) are of great importance in the agricultural economy of several emerging and developing countries. The surface-charge amphoteric characteristics will confer physical/chemical properties absolutely different to constant-charge soils. This surface reactivity will confer to them a particular behaviour in relation to the herbicide sorption, representing an environmental substrate that may become polluted over time due to intensive agronomic uses. Sorption is a key parameter to evaluate the fate and behaviour of herbicides in volcanic soils. Sorption type and kinetic sorption models are also necessary in order to develop and validate QSAR models to predict pesticide sorption on volcanic soils to prevent potential contamination of water resources. The use of solute sorption mechanism models and QSAR models for pesticide sorption in soils has contributed to a better understanding of the behaviour of pesticides on volcanic soils. This chapter is divided into five sections: Physical/chemical properties of volcanic ash-derived soils; Ionisable and non-ionisable herbicides’ fate and behaviour in soil; Kinetic sorption: mechanisms involved during sorption of ionisable and non-ionisable herbicides on VADS; Sorption of ionisable and non-ionisable herbicides on VADS; and Physical/chemical properties in QSAR models: a mechanistic interpretation

Reaktiokinetiikan oppiminen rikkakasvien torjunta-aineiden kestävän kemian avulla: tapaustutkimus tulevien kemian opettajien käsityksistä

Att lära sig grunderna i kemisk kinetik på universitetsnivå är utmanande, vilket bland annat beror på begreppens abstrakta natur och den begränsade kopplingen till vardagliga tillämpningar. Denna studie bestod av två faser. I det första steget, en inlärningsmiljö för inlärningskinetik baserad på hållbar kemi. Sammanhanget var den samhällsvetenskapliga modulen för miljökemi, som tittade på de kinetiska processerna för herbicider i vulkaniskbaserade jordar och deras potential att förorena grundvatten. Syftet med inlärningsmiljön var att bidra till utvecklingen av hållbara utvecklingsfärdigheter, att främja inlärning av kemisk kunskap i sammanhang och att utveckla vetenskapliga färdigheter. Materialet utformades för två kurser i analytisk kemi och en kurs i fysikalisk kemi i ett lärarutbildningsprogram. Effektiviteten av materialet studerades med hjälp av elevernas uppfattningar. Urvalet omfattade 22 studenter, som delades in i tre målgrupper. Materialet analyserades och klassificerades med hjälp av kvalitativ innehållsanalys med hjälp av TPASK-ramverket (Technology Pedagogical Science Knowledge). Baserat på resultaten förvärvade studenter kontextualiserad kunskap om kemi och utvecklade färdigheter och kunskaper relaterade till användning av digitala resurser och kalkylblad i ett vetenskapligt sammanhang. Denna fallstudie visar att den problembaserade inlärningsmetoden erbjuder stor potential att stödja ovanstående färdigheter.Kemiallisen kinetiikan perusteiden opettaminen korkeakoulutasolla on haastavaa, mikä johtuu mm. käsitteiden abstraktista luonteesta ja rajallisesta yhteydestä arkipäivän sovelluksiin. Tämä tutkimus koostui kahdesta vaiheesta. Ensimmäisessä vaiheessa kestävään kemiaan pohjautuva reaktiokinetiikan oppimisympäristö. Kontekstina toimi sosio-tieteellinen ympäristökemian moduuli, jossa perehdyttiin rikkakasvien torjunta-aineiden kineettisiin prosesseihin tulivuoren tuhkapohjaisessa maaperässä ja niiden mahdollisuuteen saastuttaa pohjavesiä. Oppimisympäristön tavoitteena oli myötävaikuttaa kestävän kehityksen taitojen kehittämiseen, edistää asiayhteyteen kemiatietojen oppimista ja kehittää tieteellisiä taitoja. Materiaali suunniteltiin kahdelle analyyttisen kemian kurssille ja opettajankoulutusohjelman fysikaalisen kemian kurssille. Materiaalin vaikuttavuutta tutkittiin opiskelijoiden käsitysten avulla. Otos sisälsi 22 opiskelijaa, jotka jaettiin kolmeen kohderyhmään. Aineisto analysoitiin ja luokiteltiin laadullisen sisältöanalyysin avulla käyttäen TPASK (Technology Pedagogical Science Knowledge) -kehystä. Tulosten perusteella opiskelijat hankkivat kontekstualisoitua kemian osaamista ja kehittivät taitoja ja tietoja, jotka liittyvät digitaalisten resurssien ja laskentataulukoiden käyttöön tieteellisessä yhteydessä. Tämä tapaustutkimus osoittaa, että ongelmapohjaisen oppimisen lähestymistapa tarjoaa suuren potentiaalin edellä mainittujen taitojen tukemiseen.Teaching the fundamentals of chemical kinetics on the college level is challenging to teachers and students alike due to its abstract nature of concepts and limited connection with real context applications. This study consisted of two phases starting with designing a chemistry education for the sustainable development-based learning environment of reaction kinetics, followed by a case study in which students' perceptions toward learning chemistry by solving a real environmental problem using digital resources, spreadsheets, and an active learning environment, were explored. First, we designed a Socio-Scientific Environmental Chemistry module centered on the sorption kinetic processes of herbicides in volcanic ash derived soils (VADS) and their potential to pollute groundwater. The objective of the learning module was to contribute to the development of sustainability skills, to promote learning of contextualized chemistry knowledge, and to develop scientific skills. This module employs spreadsheets as computational tools in chemistry to model real sorption kinetic data of herbicides in VADS. The learning module was designed for one section of two Analytical Chemistry courses and one Physical Chemistry course of an undergraduate chemistry teacher-training program. After the design phase, the learning module was implemented in each course, and students' perceptions were gathered using the focus group technique. The sample was of 22 students distributed into three focus groups. The data collected were analyzed and categorized through qualitative content analysis using the Technological Pedagogical Science Knowledge (TPASK) framework. On the basis of our findings, the students acquired contextualized chemistry knowledge and develop skills and knowledge related to using digital resources and spreadsheets in a scientific context. Besides, the preservice chemistry teachers' knowledge of pedagogy allowed them to develop some elements of their pedagogical science knowledge and TPASK. This case study shows that the problem-based learning approach offers great potential in supporting a learning environment suitable to working with spreadsheets to solve real-environment problems in chemistry education.Peer reviewe

Mechanistic insights into simultaneous removal of copper, cadmium and arsenic from water by iron oxide-functionalized magnetic imogolite nanocomposites

Imogolite and magnetic imogolite-Fe oxide nanocomposites (Imo-Fe50 and Imo-Fe25, at 50 and 25 % Fe loading (w/w), respectively) were synthesized and tested for the removal of aqueous copper (Cu), cadmium (Cd), and arsenic (As) pollutants. The materials were characterized by transmission electron microscopy, and specific surface area and isoelectric point measurements. The Fe-containing samples were additionally characterized by Mössbauer spectroscopy and vibrating-sample magnetometry. Significant differences were found in the morphological, electrophoretic, and magnetic characteristics between imogolite and the nanocomposites. The in-situ Fe-oxide precipitation process modified the active surface sites of the imogolite. The Fe–oxide, mainly magnetite, favored the contaminants’ adsorption over the pristine imogolite. The adsorption kinetics of these pollutants were adequately described by the pseudo-second order and intraparticle diffusion models. The kinetic models showed that surface adsorption was more important than intraparticle diffusion in the removal of the pollutants by all the adsorbents. The Langmuir-Freundlich model described the experimental adsorption data, and both nanocomposites showed greater adsorption capacity than the imogolite. The adsorption of Cu and Cd was sensitive to cationic competition, showing a decrease of the adsorption capacity when the two cations coexisted, while their adsorption increased in the presence of arsenate

Adsorption of biosolids and their main components on chalcopyrite, molybdenite and pyrite: Zeta potential and FTIR spectroscopy studies

Zeta potential measurements were used to assess the electrokinetic characteristics of chalcopyrite, molybdenite and pyrite in the presence of biosolids and their main components (humic acids, glucose and serum albumin) as well as a commercial collector (Aero 6697). Fourier transform infrared spectroscopy (FTIR) was then used to gain a deeper understanding of the interaction of these compounds with these sulfide minerals. It aims to achieve a better understanding of the surface chemistry of sulfide–water interfaces that improve froth flotation at industrial scale in the step of copper sulfide ore concentration. Zeta potential results show that hydrogen and hydroxide ions are potential determining ions for each sulfide mineral studied. The addition of 50 g/t biosolids or all the other chemicals used in this investigation shift the isoelectric point of chalcopyrite. Under the same conditions, only humic acid significantly affects the zeta potential of molybdenite, making it more negative in the pH range investigated, and shifting its isoelectric point about 6 pH units. These compounds seem to have a poor affinity with pyrite surfaces because their zeta potential is slightly modified. FTIR spectroscopy characterization shows that biosolids and their main components can interact with chalcopyrite, molydenite and pyrite surfaces through a complex mechanism involving chemical or physical linkages. The results reported here seem to indicate that biosolids may be used as new environment-friendly froth flotation agents to concentrate copper and molybdenum sulfide mineral

Determinación electroanalítica de Paratión, Dimetoato, Aldrin Dieldrin y DDT.

Se estudia el comportamiento polarográfico de pesticidas organofosforados (Paratión y Dimetoato) y de pesticidas organoclorados (DDT, Aldrin y Dieldrin), estableciéndose para cada uno de ellos las condiciones óptimas de análisis. Como técnicas analíticas se emplean la polarografía de pulso diferencial y con muestreo de la corriente, la voltametría de barrido lineal y de pulso diferencial. Para los organofosforados la mejor técnica es la polarografía de pulso diferencial, alcanzándose un límite de detección de 0,1 ppm. En el caso de los organoclorados se aplica con ventaja la voltametría de barrido lineal, usando un electrodo de carbono vítreo recubierto con mercurio y cloruro de Litio IN en dimetilsulfóxido como electrolito soporte; en estas condiciones el límite de detección para DDT es 0,96 ppm y para Aldrin y Dieldrin 3,1 y 2,7 ppm, respectivamente

Empleo del programa computacional MICROQL en la aplicación del modelo de la capacitancia constante a óxido de hierro sintético de baja cristalinidad

El programa computacional MICROQL se utilizó para calcular, a través del modelo de la Capacitancia Constante, la distribución superficial de especies, en función del pH, para un óxido de hierro sintético de bajo grado de cristalinidad. Los cálculos de distribución de especies fueron empleados para describir teóricamente las curvas de carga superficial, determinadas a partir de titulaciones potenciométricas, a distintas fuerzas fónicas. El óxido de hierro presentó una superficie específica de 305 m2 g- 1 y un número máximo de sitios de intercambio de 125 cmol kg-1. Las curvas de titulación potenciométrica se realizaron en soluciones de NaCI y KC1; no se observó un efecto de electrólito usado y de la intersección de dichas curvas se determinó un punto de carga cero de 7 ,8. Con el modelo de la Capacitancia Constante se determinaron las constantes de disociación superficiales encontrándose un pK de 6,7 y 9,6 para una superficie positiva y negativa respectivamente a fuerza fónica (1) 0,1 M; 6,0 y 10,2 para 1=0,01 M y 5,2 y 10,8 para 1=0,001 M, con las cuales se describieron perfectamente las curvas experimentales de carga superficial