Volatility of heavy metals during incineration of tannery sludge in the presence of chlorides and phosphoric acid

Knowledge of the behaviour of heavy metals in the combustion process is a most important factor in selecting disposal alternatives for waste materials. Accordingly, in this work, the vaporization behaviour of highly concentrated heavy metals (Pb, Zn, Cu and Cr) in tannery sludge were investigated experimentally. The sludge was spiked with various chlorine compounds (i.e. PVC, FeCl3, CaCl2 and NaCl) and pre-treated with phosphoric acid in order to evaluate the capacity of enhancement and weakening of the volatility of the heavy metals contained in tannery sludge. The experimental results show that the vaporization percentages increased with increasing ratio of Cl/sludge and temperature, and the accelerating and increasing effect of the addition of chlorides on the vaporization percentage of heavy metals was dependent on the release capacity of chlorine radicals. The vaporization percentages of lead and zinc increased by 15-20%, whereas those of copper and chromium increased by only about 3 and 10% at 800 degrees C. However, heavy metals were not expected to be completely released in the combustion process in spite of the high ratio of Cl/sludge. Alternately, heavy metals contained in tannery sludge can be immobilized effectively by pre-treatment with phosphoric acid. When the 85% phosphoric acid accounted for 10% of dry basis of tannery sludge, the phosphate-treated sludge showed the lowest vaporization percentage of about 3-15% with formation of Ca18Cu3(PO4)14, Ca9Cr(PO4)7, Ca19Zn2(PO4)14 and PbMgP2O7 in the bottom ash.

[Observations on the airborne fungi and their relationship to asthmatic patients in Shenyang Maluwan area]

From July 1990 to June, observations were made of the type and amount of fungi present in the air, in the Maluwan District of Shenyang City, using dish-exposure and slide-exposure as method of detection. 954 colonies of fungi were isolated with dish-exposure, consisting of 47 species; and 11,033 fungi spores were collected with the slide-exposure. Skin tests were made using 13 species of fungi allergen for 114 cases of asthmatic patients, the positive rate was 73.7%. A special desensitization therapy was given to 103 cases of asthmatic patients, the total effective rate was 86.4%, while antiasthma drugs gave an effective rate of 41.1% (P < 0.01).