The thesis discuss about the experimental activity developed between September and December 2017 in the Colombian “Zona de Reserva Campesina del Valle del Río Cimitarra” (ZRC-VRC).The project carried out by ACVC, CeTAmb LAB of the University of Brescia and UNIPAZ of Barrancabermeja aims to produce sustainable solutions for the mercury’s removal from wastewater originated by informal gold mining in the reserve’s area.Gold represent one of the most extracted materials, both in South American general terms and in local Colombian terms.Mining’s high importance, however, did not produce as much employment and general wealth as imagined and has in fact encouraged informal mining, which represents more than 60% of Colombian’s total mining activity.Without understating human rights violations related to the Artisanal and Small-scale Mining, the most worrying fact is the large use of mercury in gold amalgamation process, considering that 71% of South American anthropogenic mercury emissions comes from artisanal gold mines, with high negative health impacts for miners and their neighboring communities.The ACVC, a non-governmental social organization of “campesinos” rooted on the territory of 8 municipalities of the Magdalena Medio area with 120 Juntas de Acción Comunal, works with a participated approach on various sectors to defend the territory and its population.Within this framework the objective is to perform artisanal gold mining in a sustainable and clean way, to maintain and preserve the ZRC, to defend the health security of the community and to favor a path of legalization and legitimation of the local mines without a license.Following the evaluation of a proper phytodepuration system and a pre-treatment of chemical precipitation, in addition to the construction of a first small-scale pilot plant, and after the construction of a full-scale pilot plant, this fourth project directly follows the path of the ones before.The objective was to close this path by experimenting solutions that could increase efficiency and addressing the topics still unexplored.In order to limit the use of aluminum sulphate and its costs, sedimentation tests were carried out to evaluate, together with the reduction of sulphate, the suitability of a vegetable coagulant, Eichhornia crassipes extract: the results were positive in front of a lowering of the dosage of sulphate down to 0,001% by weight on the wastewater (efficiency >98%), even if there were no substantial changes on the clariflocculation’s processes with the addition of vegetable coagulant.For a more precise understanding of the phytodepuration compartment, was performed a 2-month monitoring of a closed system with Eichhornia crassipes plants in order to expose the plants to mercury contamination. Three distinct groups were selected: new plants, i.e. uncontaminated, plants extracted from the pilot plant (exposed to contamination for a period of about one year) and the same plants from the phytodepuration tank, washed before the experiment.With this experimentation was possible to define a general behavior of the plants and provide an evaluation of their purification cycle’s lifetime.Was also evaluated if the rate of mercury’s evapotranspiration was negligible, obtaining comforting results.About the strengthening of the purifying aspects, a first assessment was made on the possibility of adding an adsorption or filtration treatment, comparing in a column test a commercial activated carbon with a sand filter:the second presented higher performances (>99,5%) and reduced the concentration of Hg from 45,9 μg/l to 0,2 μg/l.Lastly, through the technologies available in the artisanal mine, a first test of thermal separation of mercury from contaminated plants was carried out, to reduce their environmental impact.Furthermore, was evaluated the use of thermal separation in the recovery of residual gold in the sludge of the pilot plant sediment.
La tesi tratta l’attività sperimentale condotta tra settembre e dicembre 2017 nella Zona di Riserva Contadina della Valle del fiume Cimitarra ZRC-VRC in Colombia.Il progetto portato avanti da ACVC,CeTAmb LAB e UNIPAZ di Barrancabermeja ha come obiettivo produrre soluzioni sostenibili per la rimozione del mercurio dalle acque reflue originate dall’estrazione informale dell’oro nel territorio della riserva.L’oro rappresenta uno dei materiali su cui si è investito di più sia in termini continentali sudamericani sia in termini locali colombiani.L’alta attività mineraria però ha faticato a produrre altrettanta ricchezza occupazionale e ha nei fatti favorito l’estrazione nelle miniere informali.Pur tenendo conto delle violazioni dei diritti umani legate alle miniere artigianali,preoccupa di più l’utilizzo del mercurio nei processi di amalgamazione, soprattutto dato che il 71% delle emissioni sudamericane di mercurio antropogenico ha come fonte le miniere d’oro artigianali,con alti rischi per le zone limitrofe e non.L’ACVC,organizzazione sociale contadina non governativa radicata sul territorio di 8 comuni del Magdalena Medio con 120 Juntas de Acción Comunal,porta avanti in maniera partecipata varie tematiche a difesa del territorio e della sua popolazione.In tale quadro si inserisce l’obiettivo di rendere l’estrazione artigianale dell’oro sostenibile e pulita,conservare e preservare la ZRC,difendere la salute della comunità e favorire un percorso di legalizzazione e legittimazione delle miniere locali prive di licenza.A seguito della valutazione di un corretto sistema di fitodepurazione e di un pretrattamento di precipitazione chimica,oltre alla costruzione di un primo impianto pilota a piccola scala e dopo la costruzione di un impianto pilota a scala reale,questo quarto progetto si pone in continuità con i precedenti,con l’obiettivo di chiudere il percorso svolto sperimentando soluzioni che aumentassero l’efficienza e affrontando gli argomenti ancora aperti.Per contenere l’uso di solfato di alluminio e i suoi costi sono state effettuate prove di sedimentazione per valutare, contestualmente alla riduzione del solfato,il potenziale affiancamento nel processo di un coagulante vegetale estratto di Eichhornia crassipes:i risultati sono stati positivi con un abbassamento del dosaggio di solfato fino a 0,001% in peso sul refluo (rese >98%),anche se non si sono viste variazioni sostanziali nei fenomeni di chiariflocculazione con l’aggiunta del coagulante naturale.Per osservare il funzionamento del comparto di fitodepurazione è stato svolto un monitoraggio di 2 mesi di un sistema chiuso con esemplari di Eichhornia crassipes),al fine di esporre al mercurio le piante in esame.Sono stati selezionati tre gruppi distinti: piante nuove incontaminate,piante provenienti dall’impianto pilota esposte a contaminazione per un periodo di circa un anno e una parte di quest’ultime lavata prima dell’esperimento.Si è così potuto definire un comportamento generale delle piante e fornire una valutazione sulla durata utile del loro ciclo depurativo.Si è inoltre voluto verificare con esattezza che le piante non fitovolatilizzassero mercurio, ottenendo risultati confortanti.Circa il potenziamento degli aspetti depurativi si è intrapresa una prima valutazione sulla possibilità di aggiungere un comparto di adsorbimento o filtrazione, confrontando con una prova in colonna un carbone attivo commerciale con un filtro a sabbia:quest’ultimo ha presentato rese maggiori (>99,5%) e ridotto la concentrazione di Hg nel refluo da 45,9 μg/l iniziali a 0,2 μg/l finali.Infine attraverso le tecnologie a disposizione della miniera si è effettuata una prima prova di separazione termica del mercurio dalle piante contaminate,per diminuire l’impatto ambientale dei rifiuti solidi,con una valutazione sull’uso della separazione termica per il recupero dell’oro residuo nei fanghi del sedimentatore dell’impianto pilota.
Studio sperimentale di tecnologie per la rimozione del mercurio dalle acque reflue generate da attività informali di estrazione dell’oro in Colombia
DEL VECCHIO, MICHELE
2016/2017
Abstract
The thesis discuss about the experimental activity developed between September and December 2017 in the Colombian “Zona de Reserva Campesina del Valle del Río Cimitarra” (ZRC-VRC).The project carried out by ACVC, CeTAmb LAB of the University of Brescia and UNIPAZ of Barrancabermeja aims to produce sustainable solutions for the mercury’s removal from wastewater originated by informal gold mining in the reserve’s area.Gold represent one of the most extracted materials, both in South American general terms and in local Colombian terms.Mining’s high importance, however, did not produce as much employment and general wealth as imagined and has in fact encouraged informal mining, which represents more than 60% of Colombian’s total mining activity.Without understating human rights violations related to the Artisanal and Small-scale Mining, the most worrying fact is the large use of mercury in gold amalgamation process, considering that 71% of South American anthropogenic mercury emissions comes from artisanal gold mines, with high negative health impacts for miners and their neighboring communities.The ACVC, a non-governmental social organization of “campesinos” rooted on the territory of 8 municipalities of the Magdalena Medio area with 120 Juntas de Acción Comunal, works with a participated approach on various sectors to defend the territory and its population.Within this framework the objective is to perform artisanal gold mining in a sustainable and clean way, to maintain and preserve the ZRC, to defend the health security of the community and to favor a path of legalization and legitimation of the local mines without a license.Following the evaluation of a proper phytodepuration system and a pre-treatment of chemical precipitation, in addition to the construction of a first small-scale pilot plant, and after the construction of a full-scale pilot plant, this fourth project directly follows the path of the ones before.The objective was to close this path by experimenting solutions that could increase efficiency and addressing the topics still unexplored.In order to limit the use of aluminum sulphate and its costs, sedimentation tests were carried out to evaluate, together with the reduction of sulphate, the suitability of a vegetable coagulant, Eichhornia crassipes extract: the results were positive in front of a lowering of the dosage of sulphate down to 0,001% by weight on the wastewater (efficiency >98%), even if there were no substantial changes on the clariflocculation’s processes with the addition of vegetable coagulant.For a more precise understanding of the phytodepuration compartment, was performed a 2-month monitoring of a closed system with Eichhornia crassipes plants in order to expose the plants to mercury contamination. Three distinct groups were selected: new plants, i.e. uncontaminated, plants extracted from the pilot plant (exposed to contamination for a period of about one year) and the same plants from the phytodepuration tank, washed before the experiment.With this experimentation was possible to define a general behavior of the plants and provide an evaluation of their purification cycle’s lifetime.Was also evaluated if the rate of mercury’s evapotranspiration was negligible, obtaining comforting results.About the strengthening of the purifying aspects, a first assessment was made on the possibility of adding an adsorption or filtration treatment, comparing in a column test a commercial activated carbon with a sand filter:the second presented higher performances (>99,5%) and reduced the concentration of Hg from 45,9 μg/l to 0,2 μg/l.Lastly, through the technologies available in the artisanal mine, a first test of thermal separation of mercury from contaminated plants was carried out, to reduce their environmental impact.Furthermore, was evaluated the use of thermal separation in the recovery of residual gold in the sludge of the pilot plant sediment.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/23145