Cadmium adsorption

CADMIUM ADSORPTION – 50

Metals from anthropogenic activities contaminate the environment, inputs and raw materials and, consequently, the food chain, thus reaching everyone. Due to the accumulation of these metals, as well as their harmful consequences, studies are being carried out to assess the levels reached by such contaminations. As the metal adsorption capacity by sawdust was not exhausted in the first use, the possibility of a new contact was studied, reusing the remaining solution, maintaining the proportion. In a second step, times of 12, 8 and 4 hours were tested. Cadmium content was determined by atomic absorption spectrophotometry (EAA) in the contact solution, after separation of sawdust by filtration. From the results obtained, we can say that these residues can be used as adsorbents for heavy metals in the treatment of effluents.

The constant demographic and industrial growth, added to the disorderly occupation and the inadequate use of water and soil, always results in pollution of the environment, being something to worry about.

Other forms of soil contamination are residues from

CADMIUM ADSORPTION – 51

cement manufacturing, burning fossil fuels and urban waste and sewage sediment. In agriculture, a direct source of cadmium contamination is the use of phosphate fertilizers. It is known that the uptake of cadmium by plants is greater the lower the soil pH. In this aspect, acid rain represents a determining factor in the increase in metal concentration in agricultural products.

Cadmium can interact with negatively charged groups existing in the cell wall (phosphoryls, hydroxyls, carboxyls and sulfhydryls) and, in this way, be adsorbed. The metal can also chemically interact with manoproteins and thus penetrate through the glucan layer, reaching the cytosol through transport proteins.

Sugarcane, originally from India, is currently explored in almost the entire country, which has 5.4 million hectares cultivated, considered the largest world producer and the country with the greatest potential for expansion in planted area.

These residues that remain in the soil and are not yet explored in Brazil, present quantities that vary with age, variety and location of planting, which can range between

CADMIUM ADSORPTION – 52

6 t.ha-1 and 22.8 t.ha-1 of straw. The amount of residues can reach 1/5 of the total weight of the sugarcane and, therefore, cause problems for post-harvest operations. It is estimated that, in addition to the amount of bagasse processed and used to feed boilers, there is a surplus of sugarcane bagasse corresponding to 8% in the adjacent distilleries and 12% in the autonomous ones, which could have other destinations (which have already been cited several here in this book), including being used to improve the quality of the environment.

From the results obtained with the experiment that used the concentration of 25 mg Cd.L-1 of sawdust, significant differences were observed (P< 0.05) between the four times used. The times of 8, 12 and 16 hours showed differences significant (P < 0.05) and were considered efficient as to the adsorption process of the metal present in the initial solution. In the two subsequent reuse treatments, the low adsorbed concentration was probably due to the low concentration of the metal present in the respective remaining solutions, since the probability of contact between the metal and the sawdust was lower.

CADMIUM ADSORPTION – 53

For the two waste used (sawdust and bagasse of sugar cane) the time of 4 hours proved to be insufficient to promote adsorption.

From the results obtained at the contact times of 8, 12 and 16 hours, it can be said that sawdust and sugarcane bagasse are agro-industrial residues that can be used as absorbent materials for heavy metals in the treatment of effluents, showing thus to uses in soil conservation.