Physico-chemical characteristics of some soils from Mali and their potential in heavy metal removal
Rivers, streams and groundwater contaminated by heavy metals is a growing concern world wide as the pressure on existing water resources is increasing. Unfortunately, low income countries are afflicted the most. There is a need for cost efficient and simple methods and techniques to solve the pro...
| Autor principal: | |
|---|---|
| Formato: | L3 |
| Lenguaje: | Inglés sueco |
| Publicado: |
SLU/Dept. of Soil and Environment
2008
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| Materias: |
| _version_ | 1855572023199137792 |
|---|---|
| author | Sällström, Märit |
| author_browse | Sällström, Märit |
| author_facet | Sällström, Märit |
| author_sort | Sällström, Märit |
| collection | Epsilon Archive for Student Projects |
| description | Rivers, streams and groundwater contaminated by heavy metals is a growing concern
world wide as the pressure on existing water resources is increasing. Unfortunately, low
income countries are afflicted the most. There is a need for cost efficient and simple
methods and techniques to solve the problem. Previous studies have indicated great
potential for clay minerals in pollution control. However, the studies have been carried
out on synthesized clays and through modeling predictions. The objective for this study
was to investigate natural mixed clays from Mali and their potential in heavy metal
removal.
Experiments were carried out on three natural clay samples from Mali. Using X-ray
diffraction and electron microscope the mineral composition and its morphology were
investigated. The physico-chemical properties of the mixed clays were investigated by
acid-base titrations preceded by a purification procedure. Finally, adsorption experiments
were carried out with Pb2+, Cd2+, Cu2+, Zn2+ and Cr3+ ions in aqueous suspensions.
The mineralogical analyses showed that all three clay samples mainly consisted of
crystalline quartz. According to the literature and previous modeling predictions carried
out on quartz, the pKa1 value is negative. Basically, it means that the hydrated quartz
surface has no base properties, and that the only surface sites are ≡Si-OH and ≡Si-O-. It
can therefore be assumed that rather than having a specific pHpzc the surface is neutral
over a wide pH range. pKa2 was determined through alkalimetric titrations to 9.7 which is
a value that corresponds relatively well with the literature. All clay samples proved to
completely remove Pb2+, Cd2+, Cu2+, Zn2+ and Cr3+ from aqueous solution at different pH
ranges. At pH >7, all the studied metal ions are adsorbed to the mineral surface. Since the surface is neutral at this pH it can be assumed that all metals are adsorbed to the surface as inner-sphere complexes.
Using this clay mineral for heavy metal removal requires fairly high pH values for the
water being treated. The pH has to be well above 7 to be certain that all metals are
adsorbed. For a more wide spread application of clay minerals as heavy metal adsorbents
further studies in clay mineral characterization are necessary. Every country has their
unique soils with different properties and capacities that need to be mapped. |
| format | L3 |
| id | RepoSLU12221 |
| institution | Swedish University of Agricultural Sciences |
| language | Inglés swe |
| publishDate | 2008 |
| publishDateSort | 2008 |
| publisher | SLU/Dept. of Soil and Environment |
| publisherStr | SLU/Dept. of Soil and Environment |
| record_format | eprints |
| spelling | RepoSLU122212017-11-02T09:40:59Z Physico-chemical characteristics of some soils from Mali and their potential in heavy metal removal Sällström, Märit heavy metals adsorption natural clays Rivers, streams and groundwater contaminated by heavy metals is a growing concern world wide as the pressure on existing water resources is increasing. Unfortunately, low income countries are afflicted the most. There is a need for cost efficient and simple methods and techniques to solve the problem. Previous studies have indicated great potential for clay minerals in pollution control. However, the studies have been carried out on synthesized clays and through modeling predictions. The objective for this study was to investigate natural mixed clays from Mali and their potential in heavy metal removal. Experiments were carried out on three natural clay samples from Mali. Using X-ray diffraction and electron microscope the mineral composition and its morphology were investigated. The physico-chemical properties of the mixed clays were investigated by acid-base titrations preceded by a purification procedure. Finally, adsorption experiments were carried out with Pb2+, Cd2+, Cu2+, Zn2+ and Cr3+ ions in aqueous suspensions. The mineralogical analyses showed that all three clay samples mainly consisted of crystalline quartz. According to the literature and previous modeling predictions carried out on quartz, the pKa1 value is negative. Basically, it means that the hydrated quartz surface has no base properties, and that the only surface sites are ≡Si-OH and ≡Si-O-. It can therefore be assumed that rather than having a specific pHpzc the surface is neutral over a wide pH range. pKa2 was determined through alkalimetric titrations to 9.7 which is a value that corresponds relatively well with the literature. All clay samples proved to completely remove Pb2+, Cd2+, Cu2+, Zn2+ and Cr3+ from aqueous solution at different pH ranges. At pH >7, all the studied metal ions are adsorbed to the mineral surface. Since the surface is neutral at this pH it can be assumed that all metals are adsorbed to the surface as inner-sphere complexes. Using this clay mineral for heavy metal removal requires fairly high pH values for the water being treated. The pH has to be well above 7 to be certain that all metals are adsorbed. For a more wide spread application of clay minerals as heavy metal adsorbents further studies in clay mineral characterization are necessary. Every country has their unique soils with different properties and capacities that need to be mapped. Floder och grundvatten kontaminerade med tungmetaller är ett växande problem när trycket på jordens existerande vattenresurser ökar. Tyvärr är befolkningen i låginkomstländer värst drabbade. Det finns därför ett behov av billiga och enkla metoder för att rena vatten från tungmetaller. Tidigare studier har visat stor potential för olika typer av lermineral. Dock har de flesta av dessa studier utförts på syntetiserade leror eller med hjälp av modeller vilket inte alltid ger en sann bild. Syftet med denna studie var att undersöka naturliga leror från Mali i Västafrika och deras förmåga att rena vatten från tungmetaller. Experimenten utfördes på tre olika jordprover från Mali. Röntgendiffraktion och elektronmikroskop användes för att bestämma jordens mineraluppsättning och morfologi. De fysiokemiska egenskaperna bestämdes genom syra- bastitreringar som föregicks av flera reningssteg där organiskt material, karbonater och järnoxider togs bort. Avslutningsvis utfördes adsorptionsexperiment med Pb2+, Cd2+, Cu2+, Zn2+ and Cr3+ i vattenlösning. Experimenten för mineraluppsättning och struktur visade att alla tre jordprover bestod till största delen av kristallint kvarts. Enligt litteraturen och tidigare modelleringar har kvarts ett negativt pKa1 värde. Detta betyder att den hydratiserade kvartsytan inte har några basiska egenskaper och att de enda ytpositionerna för kvarts är ≡Si-OH and ≡Si-O-. Därför kan det antas att ytan är oladdad eller neutral över ett vidare pH intervall snarare än vid ett pHpzc. pKa2 bestämdes genom bastitrering till 9,7 vilket är ett värde som stämmer relativt bra överens med tidigare publicerade värden. Pb2+, Cd2+, Cu2+, Zn2+ i vattenlösning renades med hjälp av jordproverna vid olika pH intervall. Vid pH >7, var alla de studerade metallerna adsorberade till mineralytan. Eftersom ytan på kvarts till största delen är neutralt laddad vid detta pH värde kan det antas att metallerna binder som innersfärskomplex till ytan. Att använda dessa jordar för rening av tungmetaller kräver ett relativt högt pH värde i vattnet som ska behandlas. pH måste vara över 7 för att med säkerhet veta att metallerna är adsorberade. För en vidare spridning av denna metod är det nödvändigt med fortsatta studier inom ämnet. Varje land har sina unika jordar med olika egenskaper och förmågor att adsorbera katjoner och detta behöver kartläggas. SLU/Dept. of Soil and Environment 2008 L3 eng swe https://stud.epsilon.slu.se/12221/ |
| spellingShingle | heavy metals adsorption natural clays Sällström, Märit Physico-chemical characteristics of some soils from Mali and their potential in heavy metal removal |
| title | Physico-chemical characteristics of some soils from Mali and their potential in heavy metal removal |
| title_full | Physico-chemical characteristics of some soils from Mali and their potential in heavy metal removal |
| title_fullStr | Physico-chemical characteristics of some soils from Mali and their potential in heavy metal removal |
| title_full_unstemmed | Physico-chemical characteristics of some soils from Mali and their potential in heavy metal removal |
| title_short | Physico-chemical characteristics of some soils from Mali and their potential in heavy metal removal |
| title_sort | physico-chemical characteristics of some soils from mali and their potential in heavy metal removal |
| topic | heavy metals adsorption natural clays |