Abstract: To investigate the release and immobilization characteristics of heavy metal copper in unfired bricks prepared from copper mine tailings,unfired bricks with different strength grades (MU10,MU20,MU30) were fabricated using copper mine tailings from the Shuimuchong tailings pond in Tongling,Anhui Province.The physicochemical properties were character ized by XRD,TGA,MIP and SEM.The occurrence forms of copper were determined by Tessier sequential extraction method, and continuous leaching experiments were conducted under different pH conditions (3.2,5.6,6.6) based on the NEN 7375 method to study the release behavior and long-term leaching patterns of copper ions (Cu2+).The results showed that:① With the increase of unfired brick strength grade,the proportion of cementitious materials increased,hydration products significantly increased,porosity decreased,and the microstructure became denser.② The total Cu content in copper mine tailings was 968.45 mg/kg.After solidification into unfired bricks,the residual fraction of Cu increased from approximately 17% to 96%, indicating significant immobilization efficiency.However,under acidic conditions at pH 6.6,the residual fraction decreased to 69% while the organic-bound fraction increased to 31%.③ The 20-day continuous leaching tests showed that Cu2+ leaching ex hibited a two-stage characteristic:rapid release in the early stage (0~30 h) followed by a slow approach to equilibrium.The leaching concentration increased monotonically with decreasing pH,reaching the highest value of 0.027 mg/L at pH 3.2,which was far below the limit specified in the Identification Standard for Hazardous Waste—Identification of Leaching Toxicity (GB 5085.3—2007).The release mechanism of Cu2+ was dominated by diffusion control and depletion effects,and the pseudo-sec ond-order kinetic equation could well fit the long-term cumulative leaching amount (R2>0.91),with 10-year predicted release amounts of 22.81~53.13 mg/kg.This study indicates that unfired bricks prepared from copper mine tailings can achieve effi cient immobilization of Cu2+,with good safety performance in neutral or weakly acidic environments,while protective measures are required under strongly acidic conditions.

Key words: copper mine tailings, unfired brick, heavy metal copper, immobilization characteristics, release behavior