Performance And Mechanisms For Immobilization Of Copper Ions From Aqueous Sulotions Using Clayey Dolomite

Clayey dolomite is an important type of ore existing in palygorskite clay ore. The clayey dolomite samples in this work were obtained from palygorskite ores located in Mingguang, Anhui Province and Zhenping, Henan Province, China. The morphological and mineralogical properties of clayey dolomite and its calcined product before and after reacting with copper ions were characterized and analyzed using X-ray diffraction (XRD), X Ray Fluorescence (XRF), scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). In comparison with common dolomite and palygorskite, the effects of various parameters, viz., contact time, initial pH, initial Cu(II) concentration, temperature, and ion strength, and the performance and mechanisms on copper removal by clayey dolomite were investigated by batch experiments. The structure and physical-chemistry property evolution of heat-treatment clayey dolomite and kinetics of the samples calcined at different temperatures on removal of Cu(II) from aqueous solutions were analyzed. In addition, for the sample calcined at optimal temperature, the effect of factors (solid-liquid ratio, pH, concentration) on copper removal and the performance for continuous purification of copper containing acid wastewater (pH 4.5,50mg/L) were evaluated by static experiments and dynamic column experiments, respectively. After copper removal, the samples were regenerated by a set of ammonia solutions. The results indicated that:(1) Clayey dolomite showed better performance for the removal of Cu(II) from aqueous solutions than common dolomite and palygorskite, which removed 99.6% of the initial Cu(II) concentration of 50 mg/L under optimum conditions (pH 5; t 4 h; T 30℃). The endothermic and spontaneous Cu(II) sorption process on clayey dolomite fitted the second-order equation well, which could be well described by the Freundlich isotherm, and max removal capacity for Cu(II) was 186.2 mg/g (pH 5; 30 ℃). The major mechanisms were mainly surface precipitation induced by the dissolution of minerals and mineral-water interactions and electrostatic attraction between palygorskite and the newly formed colloid [Cu2CO3(OH)2]. (2) Clayey dolomite calcined at 650 ℃, at which temperature the solid product was composed of calcite, periclase, palygorskite and dolomite, was best for removal of Cu(II) with a removal efficiency of 99.6%. The removal mechanisms were dissolution, hydration, and neutral reactions and promote the formation of copper carbonate. Cu could be extracted from clayey dolomite after copper removal by 25% (wt.%) ammonia solution with an extraction rate of 90.3%. (3) Clayey dolomite calcined at 650 ℃ was superior to natural clayey dolomite for treatment of copper containing wastewater in columns. The throughput volume was up to 2472 bed volumes (BV) and the capacity of Cu(Ⅱ) in column was calculated as 122.7 mg/g. The pH of the effluent water was in a range of 6.5-7.8.