Avaliação ambiental dos materiais estabilizados por solidificação após incorporação do lodo de indústria de curtume em matriz de cimento.

Abstract

Leather production has been increasing more and more and in its manufacture there is a high generation of solid waste. Tannery sludge is classified as class I hazardous waste because it contains heavy metals (mainly chromium) in its composition, due to the chemical substances added in the tanning step. Chromium is present in sludge and in large quantities is very harmful to living beings. It is necessary that a treatment be carried out on the tannery sludge before it is disposed of improperly. An alternative is solidification stabilization, which stabilizes the heavy metal in a cement matrix. The objective of this work was to carry out the treatment of solid waste from tannery sludge (RSLC), being evaluated by analyzes of integrity/durability and immobilization of the chromium contaminant. The technique of stabilization by solidification was used, in cement matrices subjected to different curing times (t) and different percentages of RSLC (%). The factorial design type bk (factorial) was applied with the addition of three repetitions at the central point (PtCt), composed of two factors: time (7, 17.5 and 28 days) and percentage of tannery sludge (10, 20 and 30 %). Seven experiments were carried out. The specimens were produced and then characterizations were performed, such as: humidity, total solids and their fractions, and pH. Then, compressive strength (RC), water absorption capacity (WAC), humidification and drying (U/S), total chromium and chemical oxygen demand (COD) analyzes were carried out. The solid residue of the treated tannery sludge has total solids values that ranged from 97.64 to 98.92%. Based on the analyzes carried out, it was possible to observe that all experiments obtained values greater than 1 MPa in relation to compressive strength, therefore all are approved in the integrity test with values from 12.690 to 19.384 MPa. The durability tests (CAA and U/S) were also approved, with results within the values proposed by the Standards. The treatment was confirmed in the COD test, where the gross value was 61,580 mg.kg-1, and the lowest and highest value for the treated experiments were 23,382 and 41,790 mg.kg-1, respectively, the time and the percentage of RSLC had no significant influence. In the mass balance, it was observed that all treatments had residue retention in the cementitious matrix in the three tests analyzed (COD, STV and total chromium), with the highest retentions obtained in treatments submitted to shorter curing time and lower percentage of RSL. All experiments showed efficiency in retaining the residue in the cementitious matrix, reducing the leaching of the residue into the environment. The treatments with the shortest curing time and the lowest percentage of residue showed the greatest efficiencies in retaining the contaminant. Treatment with 10% tannery sludge represents the best disposal route