The application of pHstat leaching tests to assess the pH-dependent release of trace metals from soils, sediments and waste materials

Abstract

pH is one of the key parameters that determines heavy metal mobility in soils, sediments and waste materials. In many respects leaching behaviour as reflected by the pH(stat) leaching tests provide a better means of assessing environmental impact than analysis of total elemental composition. This paper discusses the use of pH(stat) leaching tests as a tool to assess the potential mobilisation of trace metals from soils, sediments and waste materials. The possibilities of pH(stat) leaching tests are illustrated by means of different examples. The mathematical fitting of metal leaching behaviour from soils and sediments enabled a distinction between 5 groups of elements with a different leaching behaviour, which could be related to 'pools' with different reactivity. Contrary to single and sequential extractions, where pH is difficult to control, the reactivity and mobility of metals at a user-defined pH can be investigated. Moreover, the potential buffering capacity of the sample and its sensitivity to pH changes as a result of external stresses (e.g. soil acidification, liming) can be estimated. A multidisciplinary approach combining mineralogical analysis (X-ray diffraction) with chemical analysis, pH(stat) leaching tests and geochemical modelling (MINTEQA2) can provide information on the solid-phase speciation and reactivity of heavy metals in soils, sediments and waste materials. Besides the influence of pH on heavy metal leaching behaviour, additional information on heavy metal leachability and retention by the solid matrix was obtained from the kinetics of metal release during a pH(stat) test.

Adsorption and Desorption of Lead (Pb) in Sandy Soil Treated by Various Amendments

“…The effect of temperature on adsorption of Pb was also a reflection of previous studies carried outby [19][20][21][22][23]. In general, adsorbed Pb increases for SA when the temperature increases from 4 to 40°C (Figures 8-10).…”

“…On the other hand, this rate decreases in the same case for the SA as S and SQFC. Indeed, the adsorption in the first case is more pronounced when the temperature increases thus it is endothermic whereas it is exothermic for the second case, conclusions reported by different authors [18,[22][23][24].…”

“…At basic pH, precipitation of Pb compounds in the form of oxides, hydroxides, carbonates and phosphates or their complexes may compete with adsorption [22,36]. In general, the desorbed contents show that at neutral pH, ammonium acetate makes desorb less Pb than DTPA.…”

The Influence of Biomass Ash on the Migration of Heavy Metals in the Flooded Soil Profile - Model Experiment

“…Moreover, they can be actively taken up by plants [6,19,22]. Even alkalinization of soils with Ca(OH) 2 does not have to effectively restrict the migration of certain metals (e.g, copper) moving along the profi le of the migrating groundwater [40].…”

Simulação do intemperismo natural de pilhas zinco-carbono e alcalinas

“…3 A capacidade de transferência dos constituintes da fase sólida para o lixiviado (lixiviabilidade) é determinada expondo-se o material a uma solução com características conhecidas e determinando-se o grau de dissolução dos contaminantes. 4 A lixiviabilidade dos componentes depende de diversos fatores: tamanho de partícula (área superficial exposta); temperatura (solubilidade dos solutos na água); tempo de contato (estabelecimento ou não do equilíbrio de lixiviação); 3,4 agitação; relação líquido/sólido; pH (um dos fatores dominantes da mobilidade, solubilidade, complexação e retenção de metais pesados em solos, sedimentos e resíduos); 5,6 condições redox (importante quando os compostos formados na presença de oxigênio têm diferença significativa na solubilidade em relação àqueles formados sob condições redutoras); presença de agentes complexantes, CO 2 e O 2 ; presença de matéria orgânica dissolvida e em suspensão (ela influencia a biodisponibilidade e a mobilidade de metais pesados); 7,8 presença de micro-organismos (intemperismo biológico). [1][2][3]9 A extensão da liberação de constituintes de um resíduo sólido em ensaios de lixiviação é fundamental para definir: 9,10 o potencial de impacto ambiental através do transporte pela água, incluindo solo, lençol freático e contaminação de água de superfície; os riscos ecológicos e para a saúde humana a partir da disposição inadequada no ambiente; a eficácia de processos de tratamento de resíduos para disposição final; projetos e critérios de aceitação para instalação de programas de gerenciamento de resíduos; o controle de qualidade e classificação dos produtos e resíduos; o modo de degradação dos materiais dispostos no meio ambiente.…”