Influence of Gypsum Waste Utilization on Properties and Leachability of Fired Clay Brick

Wastewater treatment activities in the chemical industry have generated abundant gypsum waste, classified as scheduled waste (SW205) under the Environmental Quality Regulations 2005. The waste needs to be disposed into a secure landfill due to the high heavy metals content which is becoming a threat to the environment. Hence, an alternative disposal method was evaluated by recycling the waste into fired clay brick. The brick samples were incorporated with different percentages of gypsum waste (0% as control, 10, 20, 30, 40 and 50%) and were fired at 1050 °C using 1 °C per minute heating rate. Shrinkage, dry density, initial rate of suction (IRS) and compressive strength tests were conducted to determine the physical and mechanical properties of the brick, while the synthetic precipitation leaching procedure (SPLP) was performed to scrutinize the leachability of heavy metals from the crushed brick samples. The results showed that the properties would decrease through the incorporation of gypsum waste and indicated the best result at 10% of waste utilization with 47.5% of shrinkage, 1.37% of dry density, 22.87% of IRS and 28.3% of compressive strength. In addition, the leachability test highlighted that the concentrations of Fe and Al was significantly reduced up to 100% from 4884 to 3.13 ppm (Fe) and from 16,134 to 0.81 ppm (Al), respectively. The heavy metals content in the bricks were oxidized during the firing process, which signified the successful remediation of heavy metals in the samples. Based on the permissible incorporation of gypsum waste into fired clay brick, this study promised a more green disposing method for gypsum waste, and insight as a potential towards achieving a sustainable end product.

Assessing lead mobility rate from spent corroded and non-corroded bullets fragments on different soil types of tropical ecosystems

Lead ions mobility from spent metallic Pb bullets is under increasing scrutiny as a potential significant source of soil contamination. This study investigates effect of soil-properties types on Pb(II) mobility from spent corroded and non-corroded bullets and associated environmental risk using water, toxicity characteristic leaching procedure and synthetic precipitation leaching procedure as leaching techniques. From results, loamy soil properties (pH and organic matter-specific) apparently favored high mobility rate of Pb(II) (0.004 - 1.166 % Pb contamination) from spent bullets compared to sandy and clay soil types. Consequently, Pb(II) mobility from corroded bullet (0.035 - 1.166 %) was significant (p < 0.05) compared to non-corroded bullet (0.004 - 0.873 %) due largely to surface area differences. Percentage Pb contamination increased proportionally with bullet retention time in the different soils types. The experiment reported average decomposition rate of 6.9 g Pb/kg within a 28 weeks retention time. Leaching potential of Pb from spent bullet arising from water, toxicity characteristic leaching procedure and synthetic precipitation leaching procedure was quite significant (p < 0.05) in order of over 100 mg/L. Both toxicity characteristic leaching procedure-Pb and synthetic precipitation leaching procedure-Pb exceeded the 5 mg/L and 15 µg/L critical levels suggested by United State Environmental Protection Agency for Pb (II) mobility and hazardous classification. A significant positive correlation existed between corroded and non-corroded Pb (II) levels within each leaching solutions. Continued dissolution of metallic Pb (II) from spent Pb-bullets may be a mechanism for natural attenuation of Pb in soils. An important result of this study is the clear influence of soil properties on Pb mobility.

Leachability of Self-Compacting Concrete (SCC) Incorporated with Fly Ash and Bottom Ash by Using Synthetic Precipitation Leaching Procedure (SPLP)

Fly ash (FA) and bottom ash (BA) are some of waste generated by coal-fired power plants, which contains large quantities of toxic and heavy metals. The combustion of coal after been heated at specific temperatures and pressures in power stations produces ash. FA and BA must be properly managed and disposed without causing any harmful environmental effects. In recent years, many researchers have been interested to study on the properties of self-compacting concrete (SCC) incorporated with FA and BA but there was very limited research from the combination of FA and BA towards the environmental needs. Therefore, this study was focused in determining the leachability of heavy metals of SCC incorporated with FA and BA by using Synthetic Precipitation Leaching Procedure (SPLP). The samples were obtained from coal-fired power plant located at Peninsula, Malaysia. As such, the potential heavy metals leached out from SCC that is produced with FA as replacement for Ordinary Portland Cement (OPC) and BA as replacement for sand with the ratios from 10% to 30% respectively were designated and casted. There are eight heavy metals of concern such as As, Cr, Pb, Zn, Cu, Ni, Mn and Fe. The results show that all heavy metals were leached below the permissible limits from USEPA and EPAV except for As which is the only heavy metal that leaches in large amount even in the control specimen. This is probably due to the influence from the acidic extraction fluid, causing As to leach out in higher amounts during the extraction process. All in all, the uses FA and BA in SCC up to 20% seem to be an environmental friendly practice as far as leaching of heavy metals in the concrete is comply with the standard.

Leaching Behavior of Lead Contaminated Soil Sample by Using Sugarcane Bagasse in Stabilization/Solidification Method

Recently, Stabilization/Solidification (S/S) method has been focusing on the usage of agricultural waste as an alternative towards environmental friendly and low cost material to substitute cement. The aim of this study is to determine the leachability of lead contaminated soil by using sugarcane bagasse as partial replacement of cement in S/S method. In this study, different percentages (2.5%, 5% and 7.5%) of treated and untreated sugarcane bagasse have been utilized as a partial replacement to cement. Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) have been conducted to determine the leachability of lead contaminated soil. The results indicate that with 7.5% of treated sugarcane bagasse replacement in cement resulted significant reduction of lead contaminant in soil up to 99 % after 28 days. As a conclusion, treated sugarcane bagasse could be an alternative low cost material in the S/S method as it can significantly reduce the remediation cost normally incurred by the usage of cement.