Heavy metals recovery from printed circuit board industry wastewater sludge by thermophilic bioleaching process

Abstract

BACKGROUND: A large quantity of heavy metal contaminated wastewater sludge is produced during the treatment of printed circuit board (PCB) manufacturing wastewater. The PCB wastewater sludge containing high concentrations of heavy metals, such as Cu and Zn, increases the potential for metal recycling. Although bioleaching is indicated as a promising technology to remove metals from electronic scrap and waste PCBs, its application for metal recovery from PCB wastewater sludge is still very limited. The purpose of this study was to develop a thermophilic bioleaching process operated in a sequencing batch reactor (SBR) to recover heavy metals from PCB wastewater sludge. RESULTS:The results show that an increase in sludge solid content from 0.5 to 5% (w/v) decreased the rate of pH reduction during the bioleaching process. It was also found that the efficiency and rate of metal solubilization decreased with increasing sludge solid content. At a sludge solid content of 0.5% (w/v), after four repeated feed/decant cycles with 10 days per cycle (40 days) of SBR operation, the maximum efficiencies of metal solubilization in the treated sludge were 65% and 100% for Cu and Zn, respectively. CONCLUSION: The solubilization efficiency of heavy metals was lower during SBR operation with a longer 20-day cycle time. Therefore, a shorter 10-day cycle time for SBR operation is preferred for the thermophilic bioleaching of PCB wastewater sludge. In the treated sludge, the potential mobility and environmental risks of heavy metals were decreased significantly after the thermophilic bioleaching process.

Selective Copper Recovery by Acid Leaching from Printed Circuit Board Waste Sludge

“…In Stage 2, a critical amount of sulfuric acid was already consumed in the previous stage, and reducing the acidity from initially pH 0.56 to 2.24 (after 10 min), and 2.43 (after 60 min) resulted in the precipitation of iron hydroxides from ferric ion, following Equation (14). Ferric ion can dissolve copper metal following Equation (15) [28], having a smaller free Gibbs energy and lower reaction rate in comparison to Equation (9).…”

“…Sulfuric leaching followed by the Jarosite process could extract 93% of Cu and remove Fe as the phase of KFe 3 (SO 4 ) 2 (OH) 6 , and later recover Cu using sulfide precipitation, which is suitable for application of pyro-metallurgy process [13]. An alternative approach by bioleaching using thermophilic sulfur-oxidizing bacteria could obtain around 65% Cu after four cycles (40 days) in a sequencing batch reactor [14]. The most challenging issue for hydrometallurgical processes is the separation of copper from iron, which involves several leaching stages, applying ultrasound, using oxidants, or precipitating agents.…”

Effects of Solid Content and Substrate Concentration on Bioleaching of Heavy Metals from Sewage Sludge Using Aspergillus niger

“…Therefore, it is crucial to develop an effective method for removing heavy metals from sewage sludge prior to its land application. To this end, the bioleaching process has been introduced as a promising, cost-effective and environmentally friendly approach for removing heavy metals from sludge, soil and sediment [8][9][10][11][12].…”

A diamino based resin modified silica composite for the selective recovery of tungsten from wastewater

“…In the nonthermal method, the wastes are initially recycled through grinding and then the metallic parts are separated from the scraps. Further, they are processed by leaching with acid and/or base to precipitate out the precious metals . The effluent of one such PCB recycling unit was found to contain some metal ions along with tungstate, W(VI) .…”