Julia Ayala

Asturian fly ash as a heavy metals removal material

Abstract Coal-burning plants produce large amounts of fly ash as a residue. Fly ash has been used in construction, agriculture, metal recovery and water pollution control. This paper considers the efficiency of fly ash in the removal of heavy metals (Cd and Cu). The fly ash is shown to be an effective metal adsorbent for these two metals. Adsorption capacity increases as metal initial concentration decreases. The removal phenomenon appears to be that the fly ash neutralises the metal solution due to its alkaline nature. The presence of high ionic strength, or appreciable quantities of Ca and Cl ions does not have a significant effect on the adsorption of these metals by fly ash.

Synthesis of three commercial products from Bayer electrofilter powders.

Electrofilter powders, a by-product of the Bayer process for the production of alumina from bauxite, were leached with sulphuric acid to dissolve gibbsite and transition aluminas, thus obtaining a commercial aluminium sulphate solution and a solid residue. This residue is treated again under more drastic conditions with sulphuric acidic in a furnace at a higher temperature, is then leached with water and filtered, a small amount of solid remaining (alpha-alumina). The liquid is a highly acidic aluminium sulphate solution which does not fulfil commercial grade specifications; the liquor is accordingly treated with potassium hydroxide or ammonium hydroxide to obtain potassium or ammonium alum. Experimental tests were conducted to investigate the synthesis of alum by crystallization. The effects on alum formation of various operating conditions, including the amount of potassium or ammonium hydroxide, temperature and seed alum dosage, were examined. The crystallization process was found to be quite effective in obtaining alum.

Production of zirconia powders from the basic disintegration of zircon, and their characterization

Monoclinic ZrO2 has been prepared through the decomposition of ZrSiO4 with soda ash and lime, followed by leaching in hydrochloric acid and sodium hydroxide. The resulting zirconia powders are characterized in terms of their physical and chemical properties.

Successful sulfur recovery in low sulfurate compounds obtained from the zinc industry: Evaporation–condensation method

The improvement of an evaporation-condensation method allows for successful recovery of elemental sulfur from sulfide concentrates from the zinc industry. Elemental sulfur can be obtained with this method in samples with a low (60%) sulfur content. The effects of heating temperature between 150°C and 250°C and heating time up to 120min on the recovery of sulfur are also studied. Elemental sulfur obtained in this way is of high purity and therefore, there is no need for further purification. The treatment of these industrial residues would help removing sulfur from the environment.

New trends in characterizing industrial bayer aluminas

This study reviews the minimum study necessary to characterize Bayer alumina for the reduction to aluminum. Several industrial-grade aluminas from a smelter in Spain are characterized in terms of surface area, gibbsite and alpha-alumina contents, bulk density and pycnometer density. Characterization results are correlated with particle size data, and different methods to measure those properties are reviewed. Finally, a minimum number of physico-chemical properties are selected to describe accurately and economically the quality of smelting-grade aluminas.

Treatment of mining waste leachate by the adsorption process using spent coffee grounds

ABSTRACT The removal of heavy metals from mining waste leachate by spent coffee grounds has been investigated. In synthetic solutions, metal uptake was studied in batch adsorption experiments as a function of pH, contact time, initial metal concentration, adsorbent concentration, particle size, and the effect of co-ions (Na, K, Ca, Mg, Cu, Cd, Ni, Zn). Results showed that adsorption was significantly affected by pH, showing the highest affinity within a pH range of 5–7. Sorption of heavy metals reached equilibrium in 3 h. Removal percentages of metals ions increased with increasing dosage. Particle size did not have a significant influence on metal uptake. The adsorption of heavy metals was found to fit Langmuir and Freundlich isotherms. Maximum Zn, Cd and Ni uptake values were calculated as 10.22, 5.96 and 7.51 mg/g, respectively, using unwashed coffee grounds (UCG) as the adsorbent and 5.36, 4.28 and 4.37 mg/g when employing washed coffee grounds as the adsorbent. The presence of co-ions inhibited the uptake of heavy metals, divalent ions having a more negative effect than monovalent ions. The results obtained in the experiments with mining waste leachate showed that UCG is effective in removing heavy metals.