The Case Of Hazardous Waste Into Arsenic Gypsum Process Of General Solid Waste

The properties, source, pollution and treatments of arsenic were discussed in the thesis. The arsenic gypsum from sulfuric acid plant and the self-made arsenic gypsum in laboratory were stabilized via the crystal transformation and medicament stabilization. The effects of the both stabilized treatments were compared. Single factor experiment and orthogonal experiment were designed to study the effect of various factors on the stabilization. The stabilized effect of arsenic gypsum was assessed based on the solid waste leaching toxicity detection method (HJ/T299-2007). The leaching performance was studied with the horizontal oscillation in sulfuric acid and nitric acid in order to provide the theoretical basics of risk assessment and harmless disposal of the hazardous waste-arsenic gypsum.The results of leaching experiments showed that, without stabilization, the concentrations of arsenic gypsum residue which content werel.3%,2.8%,5.8% and 7.2% were 8.0 mg·L-1,12.0 mg·L-1,25.6 mg·L-1 and 52.5 mg-L"1 tested in Toxicity Characteristic Leaching Procedure。 The results of the test were more than 5 mg·L-1, so they were belong to hazards waste. The arsenic concentration in arsenic gypsum residue were reduced significantly with the two kinds of stabilized treatments.The crystal transformed treatment with the reaction condition of 140 ℃,140 ℃,200℃,250℃ and 5 h. After the crystal transformed treatment, the concentration of toxic leaching arsenic were 4.1 mg·L-1,4.25 mg·L-1,3.9 mg·L-1 and 4.5 mg·L-1.They were all turned into general solid waste.In the experiment of Ferric stabilization, the molar ratio of the iron-arsenic is a major factor. When the reaction time was 15 min, the temperature was 30 ℃, pH 6.86, we could achieve a better stabilizing effect, processing of arsenic were 1.3%,2.8%,5.8% and 7.2% of arsenic gypsum, sulfuric acid required Optimization of the molar ratio of the iron-arsenic iron 1,1,2.5 and 3. After treatment of four plaster arsenic leaching toxicity of arsenic concentration was followed by 1.27 mg·L-1,4.23 mg·L-1,4.1 mg·L-1 and 7.2 mg·L-1. PFS optimization iron arsenic molar ratios of 1,1,2 and 2.5. After treatment gypsum four arsenic leaching toxic arsenic concentrations were 1.13 mg·L-1,1.23 mg·L-1, 3.3 mg·L-1 and 3.78 mg·L-1. By the leaching toxicity results, the arsenic content of 6% or less of arsenic gypsum, the higher of the As content,the higher of iron-arsenic molar ratio was needed. But when the arsenic content was more higher, it could not achieve the desired effect when used ferric sulfate as a stabilizing agent for stabilization treatment. The PFS can cause the arsenic levels in 1 to 7% of arsenic plaster into general solid waste.Crystal Transformation stabilization and stabilization of iron salts could be used to stabilize arsenic-containing plaster. Crystal transformation stabilization needed a long time, high temperature, complex operation. Via the virtue of short reaction time and high reaction speed, iron salt stabilization is relatively easier to achieve industrialization.