Heavy metals and metalloids are dangerous because they have the tendency to bioaccumulate in biological organisms over a period of time. However, it is conceived that a number of phytochemical agents as well microorganism can act as heavy metal removing agent both from human beings and the environment surrounding. For instance, microbes are used for the removal of heavy metals from the water bodies including bacteria, fungi, algae and yeast. This review shows that bacteria can play an important role in understanding the uptake and potential removal behaviour of heavy metal ions. The bacteria are chosen based on their resistance to heavy metals (incl. their toxicities) and capacity of adsorbing them. Due to specific resistance transfer factors, cell impermeability is drastically inhibited by several ion (i.e. mercury, cadmium, cobalt, copper, arsenic) forms. Between these elements, free-ion cadmium and copper concentrations in the biological medium provide more accurate determination of metal concentrations that affect the bacteria, than with most of the other existing media. Metal toxicity is usually assessed by using appropriate metal ion chelators and adjusting pH factor. Bacteria and metals in the ecosystem can form synergistic or antagonistic relationships, supplying each other with nutrients or energy sources, or producing toxins to reduce growth and competition for limiting nutritional elements. Thus, this relation may present a more sustainable approach for the restoration of contaminated sources.
This study investigated the effect of Portland cement on stabilization of heavy metal contaminated clayey soils that may give range of geo environemntal benefits. The absolute concentration of heavy metals: Lead (Pb), Zinc (Zn), Chromium (Cr), Cadmium (Cd) and Copper (Cu) were measured using an inductively coupled plasma atomic emission spectroscopy (ICP-AES). A series of laboratory scale experiments such as unconfined compression test (UCT), pH test and synthetic precipitation leaching procedure (SPLP) were performed to study the effects of curing time and cement content on the unconfined compressive strength (UCS) and leaching characteristics of heavy metals. According to results, excessive concentration of heavy metals are present in the topsoil of Shanghai Jiao Tong University (SJTU) among which Pb, Zn and Cd were most prominent. Other test results showed that the dry density of both C4 and C8 soil samples increases with curing time. Similarly the compressive strength (qu)of C4 and C8 samples at 21 d of curing increases by 40% (113 kPa-288 kPa) and 15% (745kPa-864 kPa) respectively, as compared to the 7 d of curing. Besides, the test results showed a prominent decrease in the leached concentration of heavy metals with increasing curing time.
Cadmium is one of the transition metals, known by the scientific name Cd. One of its main characteristics is the high toxicity, even in very little amounts. Cadmium is often released through industrial effluents, pesticides, chemical fertilizers, and the burning of fossil fuels. Since the presence of cadmium ions in the living organisms’ body, especially humans, can cause serious damage to the liver and pancreas, and also because its role in causing cancer has been proven, measuring very low amounts of this metal is of high importance. In the first step, this study has reviewed and analyzed common laboratory methods for measuring small amounts of cadmium. Then, according to economic, environmental, feasibility, speed, and accuracy factors, all available methods were evaluated using the ELECTRE technique. The results showed that the extraction methods using Dowex Optipore V-493 resin and extraction system in Triton X-114 surfactant, placed in the first and second positions.
Cadmium is naturally present in the mineral cadmium sulfide which is a rare form of this element and the highest amount of cadmium is obtained from the extraction process of other minerals such as lead, copper and zinc. The release of this metal into the environment leads to widespread epidemiological effects. Therefore, measuring small amounts of this metal is also of particular importance. Small amount measuring methods of this metal are such as,preconcentration using solid phase extraction system using adsorbents. The main part of the preconcentration process is achieved by adsorption processes. In this study, the behavior of Freundlich and Langmuir adsorption isotherms for the capacity of TMON and IMNM adsorbents in cadmium adsorption has been evaluated by Power and Rational statistical distributions. At the end of the study, the constant coefficients of the Freundlich and Langmuir models were compared in both linear and non-linear modes. The results showed; the linearization method for the Kf coefficient of the Freundlich isotherm can cause errors equal to 41.6% in TMON adsorbent and 39.3% in IMNM adsorbent. Also, in parameter b, errors of 66.66% are obtained in TMON adsorbent and 32.45% in IMNM adsorbent.
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