Kidney damage has long since been described to be the main problem for patients chronically exposed to cadmium . As mentioned above, cadmium reaches the kidney in form of cadmium-metallothionein (Cd-MT). Cd-MT is filtrated in the glomerulus, and subsequently reabsorbed in the proximal tubulus. It then remains in the tubulus cells and makes up for the major part of the cadmium body burden. The amount of cadmium in the kidney tubulus cells increases during every person’s life span. An increasing cadmium load in the kidney is also discussed to result in a higher calcium excretion, thus leading to a higher risk of kidney stones.
REMOVAL OF CADMIUM USING MEMBRANE TECHNOLOGY
Membrane technology is a generic term for a number of different, very characteristic separation processes. Membranes are used more and more often for the creation of process water from groundwater, surface water or wastewater. Membranes are now competitive for conventional techniques.The membrane separation process is based on the presence of semi permeable membranes.
Membrane filtration which is classified into microfiltration (MF), ultrafiltration (UF),nanofiltration (NF) and reverse osmosis (RO) is a pressure driven process in which the membrane acts as a selective barrier to restrict the passage of pollutants such as organics, nutrients, turbidity, microorganisms, inorganic metal ions and other oxygen depleting pollutants, and allows relatively clear water to pass through. The processes operate without heating and therefore use less energy than conventional thermal separation processes such as distillation, sublimation or crystallization. The separation process is purely physical and both fractions (permeate and retentate) can be used. Cold separation using membrane technology is widely used in the food technology, biotechnology and pharmaceutical industries. Depending on the type of membrane, the selective separation of certain individual substances or substance mixtures is possible. Important technical applications include the production of drinking water by reverse osmosis filtrations in the food industry, the recovery of organic vapours such as petro-chemical vapour recovery and the electrolysis for chlorine production.
In waste water treatment, membrane technology is becoming increasingly important. With the help of ultra/microfiltration it is possible to remove particles, colloids and macromolecules, so that waste-water can be disinfected in this way.
Reverse osmosis (RO) and nanofiltration (NF) are relatively new processes, which were initially developed for the production of potable water from saline and brackish water .
Membrane techniques like RO, NF, UF and ED are more often applied to remove of heavy metals from water solutions in the industrial scale. The removal efficiency of individual heavy metals by RO was high and amounted to 98% for Cu and 99% for Cd, while for NF it was above 90%.The application of ED for the recovery of metals for electroplating with such metals as Au, Pt, Ni, Ag, Pd, Cd, Zn and Sn/Pb from diluted electroplating wastewaters has been gaining attention. The disadvantage of ED is the inability to remove simultaneously the non-ionic substances from the dilute stream.Electrodialytic removal of Cd(II) from wastewater sludge. During the remediation a stirred suspension of wastewater sludge was exposed to an electric dc field. The liquid/solid (mL/g fresh sludge) ratio was between 1.4 and 2. Three experiments were performed where the sludge was suspended in distilled water, citric acid or HNO3 . The Cd(II) removal in the three experiments was 69%, 70% and 67%, respectively.Montmorillonite, kaolin, tobermorite, magnetite, silica gel and alumina that removed more than 80% from a solution of initial concentration range 1–100 ppm for cadmium For the nanofiltration (NF) membrane, research showed removal efficiencies around 97% for cadmium (initial concentration C0 = 500 ppm), UF membranes to remove Cd(II) and Cr(III) ions from synthetic solution. The highest capacity for Cd(II) using sugar- cane bagasse treated with triethylenediamine. This high capacity was caused by a greater number of nucleophilic sites as a result of chemical modification by the triethylenetetramine. Another modified plant waste adsorbent used for removal of Cd(II) is Eucalyptus bark. In this study the influence of temperature on the sorption isotherms of cadmium was also been studied. When the temperature was raised from 20 to 50 C, the sorption capacity increased.
Aluminium oxide is also beneficial in terms of efficiency and economy. This study illustrated that the amount of adsorbed cadmium ion increased with initial metal concentration, contact time and with the solution pH but decreased with adsorbent dosages or masses.