Study on the mercury removal performance and strengthening method of high sulfur and iron content textile dyeing sludge char

Pyrolysis char was prepared from high sulfur and iron content textile dyeing sludge. The combined states of S and Fe in the samples before and after pyrolysis and the removal characteristics of Hg⁰ by pyrolysis char were studied. The performance of Hg⁰ removal was improved by air oxidation and ZnCl₂ impregnation. The results showed that S in sludge was divided into sulfate, sulfide, and organic sulfur. Fe existed as Fe³⁺ and Fe²⁺ compounds. After pyrolysis, inorganic sulfur was transferred to organic sulfur and Fe³⁺ was transferred to Fe²⁺. Most S and Fe were retained in pyrolysis char and some formed pyrrhotite (Fe_1−xS). The specific surface area of raw char was small and had a certain Hg⁰ removal capacity, dominated by chemical adsorption. When the air oxidation time was controlled within 12 h, the Hg⁰ adsorption capacity of pyrolysis char at high temperature (≥600 ℃) was increased by more than 46%. During pyrolysis of ZnCl₂ impregnated sludge, more S was fixed in pyrolysis char to generate ZnS. The Hg⁰ adsorption capacity of ZnCl₂ modified char pyrolyzed at 600 ℃ reached 28.71 μg/g in 30 min. With air oxidation, the Hg⁰ removal efficiency was further improved. After oxidation for 12 h, the Hg⁰ adsorption capacity was 43.75 μg/g.