As an environmentally hazardous waste, blast furnace (BF) flue dust had a potential to reduce CO2 emission if recycled as fuels or reducing agents due to the high carbon content. The structure of carbon was a principal factor to the reactivity of carbon conversion and therefore was highly relevant to efficient utilization. In this work, the characteristics and chemical structures of carbonaceous materials in BF flue dust were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared, and Raman analysis. The results showed that the aromatic structure of crystalline carbon was dominant in carbonaceous materials. Polymeric aromatic carbon and oxygen-containing groups (epoxide and esters carbon) existed on the surface. The stacking height (L c ), the in-plane crystallite sizes (L a ), and the interlayer spacing (d 002) of the aromatic structure layer were 2.45, 3.31, and 0.347 nm, respectively. The mass ratios of chars and cokes to carbonaceous matter were estimated to be 90.56% and 9.44%, respectively, by Raman spectroscopy. Then, the combustion reactivity was studied by thermogravimetric analysis using the Kissinger–Akahira–Sunose kinetics method. The activation energy as a function of conversion degree was determined. The results thus provided fundamental information for the utilization of BF flue dust for thermochemical conversion.

Printed circuit boards (PCBs) contain both valuable metals and hazardous materials, thereby rendering them attractive secondary sources of metals, but also environmental contaminants. Thus, we herein report the use of supergravity separation for the recovery of copper (Cu) and the concentration of precious metals present in waste PCBs. At an optimized temperature of 1300 °C, a gravity coefficient of 1000, and a separation time of 5 min, the total recoveries of Cu, Zn, Pb, and Sn over the whole separation process were 97.80%, 95.59%, 98.29%, and 97.69%, respectively. Compared with the amounts of precious metals present in the original PCBs, the contents of Ag, Au, and Pd in the Cu alloy increased by 5.16, 2, and 1.85 times, respectively, while those in the final residues increased by 2.92, 1.59, and 1.54 times, respectively. Upon combination of the appropriate hydrometallurgical process and supergravity separation of metals or alloys, this clean and efficient process provides a new way to recycle valuable metals and effectively prevent environmental pollution from PCBs.

As an environmentally hazardous waste, silica fume was considered as a potential alternative for cement and SiO 2 production. The structure of Si-O was highly relevant to the reactivity of Si conversion for efficient utilization. In this study, the characteristic and chemical structure of Si-O in silica fume were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). Deconvolution of XPS and FTIR spectra into elementary profiles was carried out to analyze the structural components. As a result, the valence state, bonding structure and elementary unit in the Si-O network of silica fume were determined. Then, the reactivity silica fume with alkali solution was studied involving the effects of NaOH concentration and temperature. The staged kinetics behavior was associated with the structure of Si-O bonds, and the activation energies were determined. The results thus provided fundamental information for the utilization of silica fume for SiO 2 production and geopolymer.

As an environmentally hazardous waste, electric arc furnace (EAF) dust had a potential to provide a wider resource of potassium if recycled due to high potassium content. In this study, the chemical and mineralogical characteristics of the EAF dust, especially the existing state of potassium, were analyzed. The results showed that the dust consisted dominantly of manganese oxides (Mn 3 O 4 , MnO, MnO 2 ) and manganese silicate (MnSiO 3 ). The K element existed in the dust was in the form of potassium permanganate (K 2 Mn 4 O 8 , insoluble) and potassium sulfate/sulfite (soluble). Then the soluble potassium salts in the dust were recovered by water leaching and crystallization. The recovery ratio of K reached 88.2%, and the products K 2 SO 4 and KCl with the K 2 O content of 65.25% were obtained. During leaching, the Mn 3 + and Mn 4 + components were reduced to Mn 2 + by sulfide (S 2 − ) or sulfite (SO 3 2 − ), and the S 2 − and SO 3 2 − components were oxidized to SO 4 2 − . The leaching kinetics was studied by the specific electrical conductivity method. The apparent activation energy was 7.76 ± 0.65 kJ/mol, suggesting that the rate controlling step of leaching process was the diffusion of K + through the diffusion layer.

As mining waste, alunite is a potential resource to produce potassium salt. The decomposition of alunite is closely associated with the recovery of soluble potassium. In this study, the effect of CaO on phase transformation of alunite in the desulfation stage was examined. The results showed that CaO was beneficial to the desulfation of alunite. The decomposition temperature to obtain soluble potassium salt (K2SO4) was reduced from 800 °C to 700 °C by adding CaO. When the mass ratio of CaO/alunite was 0.1, 81% of soluble potassium was extracted by water leaching after calcination at 700 °C for 2 h. The mechanism of CaO to promote the disintegration of alunite was proposed through analyzing the phase transformation sequences. Alkaline Ca ion was inclined to bond with acidic [SO4] groups, and thus the breakage of S–O linkages between [AlO6] octahedron and [SO4] tetrahedron were improved. Monomer [SO4] tetrahedrons were released to form K2SO4 at a lower decomposition temperature. With the increase of the amount of CaO, the excess CaO bonded with neutral Al. [AlO6] tetrahedrons in alunite transformed into [AlO4] octahedrons due to the breakage of the Al–O network. Al3+ was dissociated and bonded with [SO4] tetrahedron to form soluble Al salts.