Gas quantity and composition from the hydrolysis of salt cake from secondary aluminum processing

Understanding landfill gas behavior at elevated temperature landfills

Landfill gas (LFG) wellhead data were compared to understand the range of observations due to unique conditions at five elevated temperature landfills (ETLFs) in the U.S. Correlations of the primary gas ratio, CH4:CO2, show distinct compositional indicators for (1) typical operation, (2) subsurface exothermic reactions (SERs), (3) high moisture content, and (4) air intrusion that can help operators and regulators diagnose conditions across gas extraction wells. ETLFs A, B, D, and E showed similar trends, such as decreasing CH4 and increasing CO2, CO, and H2 that have been previously described. ETLF C uniquely exhibited elevated CH4 and temperatures simultaneously due to carbonation (i.e., CO2 consumption) of a steel slag which was used as alternative daily cover (ADC). At the maximum gas well temperature, T = 82 °C/180 °F, CH4 and CO2 concentrations were 47% and 28%, respectively. At ETLFs A, B, and E, H2 > 50% were regularly observed in affected gas wells for several years. At the five ETLFs, maximum CO concentrations ranged from 1400-16,000 ppmv. Like the analysis of CH4:CO2, it is hypothesized here that H2 (%):CO (ppmv) may infer the types of waste that are thermally degrading. Co-disposal of industrial wastes and MSW and the use of potentially reactive ADCs should remain an important consideration for landfill operators and regulators because of their potential long-term impacts to LFG quality.

Reduction for heavy metals in pickling sludge with aluminum nitride in secondary aluminum dross by pyrometallurgy, followed by glass ceramics manufacture

Secondary aluminum dross (SAD) from aluminum industry is classified as a hazardous solid waste due to containing aluminum nitride (AlN). In this work, AlN was first used to reduce heavy metals by pyrometallurgy. The reduction rates for iron, chromium and nickel were up to 90%, 80% and 100%, respectively. However, the reduction from AlN and oxygen oxidization of AlN occurred simultaneously. AlN which formed solid solution with alumina could reduce heavy metals, while the rest was oxidized by oxygen. In addition, the reduction rates for iron and chromium could be increased with increasing CaF₂ from 6.7 to 9.0 wt%. CaF₂ could decreased viscosity of molten slag, which favored the ion migration, and then increased the reduction rates. After the reduction, glass ceramics were manufactured from the molten slags. The bending strength, microhardness and alkali resistance of the glass ceramics were up to 77 MPa, 1011 HV and 98.7%, respectively. According to XRD and SEM results, glass ceramics with CaAl₂SiO₆ crystal phase, crosslinked network structure grains and smaller pores exhibited better bending resistance. In addition, glass ceramics with CaAl₂SiO₆ crystal phase possessed the highest microhardness and alkali resistance. After this process, hazardous pickling sludge and SAD were totally recycled.

Harmless disposal and resource utilization for secondary aluminum dross: A review

Secondary aluminum dross (SAD) is solid waste of primary aluminum dross extracted aluminum, which contains approximately 40-60 wt% alumina, 10-30 wt% aluminum nitride (AlN), 5-15 wt% salts and other components. The salts include sodium chloride, potassium chloride and fluorine salts. SAD has dual attributes as resource and pollutant. SAD landfill disposal has the disadvantages of occupying land, wasting resources, a high cost and great environmental impact. SAD utilization methods are currently pyrometallurgy and hydrometallurgy. In pyrometallurgy, AlN is oxidized and the salts are evaporated at high temperature. After mixing, molding and calcination, firebricks and ceramics can be manufactured from SAD. In hydrometallurgy, AlN is hydrolyzed and salts are dissolved in water. After dissolving, filtrating, precipitating, washing and calcination, γ-Al₂O₃ can be prepared from SAD. Resource consumption and emission from both utilization methods were assessed. A ton of magnesium aluminum titanate based ceramics by pyrometallurgy consumes 1043 kg raw materials and releases 69 kg of waste gas, 4.17 t of waste water and no solid waste. A ton of γ-Al₂O₃ by hydrometallurgy consumes 3389 kg raw materials and releases 111 kg of waste gas, 12.98 t of waste water and 267 kg of solid waste. Therefore, the resource consumption and emission of SAD utilization by pyrometallurgy is lower than that by hydrometallurgy. We should focus on reducing the emission of the three wastes from pyrometallurgy. We are sure that SAD can be utilized for glass ceramics by pyrometallurgy. AlN and salts can be transformed into alumina and glass phases at high temperature with no emission. We should clarify mechanisms for SAD composition adjustment to lower the glass ceramics' melting point, AlN and salts transformed into alumina and glass phases respectively, and nucleation and crystal growth of glass ceramics at high temperature.