There have been a number of studies considering the possibility of removing and recovering heavy metals from diluted solutions. These are due, principally, because of the commercial value of some metals as well as in the environmental impact caused by them. The traditional methods for removing have several disadvantages when metals are present in concentrations lower than 100 mg/l. Biosorption, which uses biological materials as adsorbents, has been considered as an alternative method. In this work, variables like pH and biomass chemical pretreatment have been studied for its effect on the capacity for zinc biosorption by Thiobacillus ferrooxidans. Also, studies to determinate the time for zinc adsorption were carried out. Results indicate that a capacity as high as 82.61 mg of Zn(II)/g of dry biomass can be obtained at a temperature of 25°C and that the biosorption process occurs in a time of 30 min.List of symbols q max Maximum capacity (mg/g)Initial concentration (mg/l)
IntroductionCurrent technologies for removal and recovery of both toxic and industrial interest metals usually produce wastes with high concentrations of them. These wastes are an important source of environmental pollution. The pollution of water, air and soil by heavy metals is one of the most important environmental problems, and of the most dif®cult ones to solve. Heavy metals usually form compounds that can be toxic, carcinogenic or mutagenic, even in very low concentrations. It has been established that of all metals or elements with metallic characteristics, 30 can form compounds that are toxic to man [1].Toxic organic compounds can be degraded to CO 2 , water and salts by biological and chemical means. On the other hand, metals are permanent and the only way of diminishing their toxicity is by changing their chemical or physical state by means of oxidation/reduction reactions, solubilization, precipitation, etc.The most common sources of water pollution with heavy metals are the petroleum processes, energy generating plants, electrodeposition of metals and metallurgic processes.So far, there have been a number of studies considering the possibility of removal and recovery heavy metals from diluted solutions. These are based, principally, in the commercial value of some metals as well as in the environmental impact caused by them. The traditional methods for removing include precipitation, oxidation/ reduction, ionic exchange, ®ltration, electrochemical processes, membrane separations, and evaporation. These methods have several disadvantages like high cost, incomplete removal, low selectivity, high energy consumption, and they generate toxic slurries that are dif®cult to eliminate. These methods are unsuitable, especially when metals are present in concentrations lower than 100 mg/l [2, 3].Alternative methods of metal removal and recovery based on biological materials have been considered [4,5]. Certain types of microbial biomass can retain relatively high quantities of metals by means of passive processes known as biosorption, which is...
