Guangwen Zhang

Removing inorganics from nonmetal fraction of waste printed circuit boards by triboelectric separation.

Metals recycling from WPCBs has been studied for a long time, which results in the appearance of many proven techniques. However, the nonmetal fraction in WPCBs has not been fully recycled due to hybridpropertiesof inorganic and organic composition. In order to improve the usability of the nonmetal fraction from WPCBs, nonmetal materials separation by using a laboratory triboelectric separation system was carried out to improve the reuse efficiency of WPCBs nonmetal fraction. The optimum tribocharger material was investigated by using the charge-mass ratio measurement system, and PMMA is the optimum tribocharger material compared with PVC, PPFT, PPR, SS. The effects of airflow, voltage and feed rate on triboelectric separation were investigated. The product LOI of positive plate is up to 77.26% with recovery rate of 25.49%, while the product LOI of negative plate is down to 47.35% with recovery rate of 35.37%, and the remove rate of inorganics is up to 43.02% by triboelectric separation. The analysis results of X-ray diffraction indicate that the main inorganic materials mixed in nonmetal fraction are SiO2, Al2O3, CaO, Cu, Fe, Sn. The X-ray fluorescence analysis shows that the triboelectric separation can effectively remove the content of SiO2 and Al2O3. The scanning electron microscope images show that inorganics tribocharge positively and distribute in product collection grooves that close to negative plate.

Triboelectric separation technology for removing inorganics from non-metallic fraction of waste printed circuit boards: Influence of size fraction and process optimization.

Removing inorganics from non-metallic fraction (NMF) of waste printed circuit boards (WPCBs) is an effective mean to improve its usability. The effect of size fraction on the triboelectric separation of NMF of WPCBs was investigated in a lab triboelectric separation system and the separation process was optimized in this paper. The elements distribution in raw NMF collected from typical WPCBs recycling plant and each size fraction obtained by sieving were analyzed by X-ray fluorescence (XRF). The results show that the main inorganic elements in NMF are P, Ba, Mn, Sb, Ti, Pb, Zn, Sn, Mg, Fe, Ca, Cu, Al and Si. The inorganic content of each size fraction increased with the size decreasing. The metal elements are mainly distributed in -0.2mm size fraction, and concentrated in middle product of triboelectric separation. The loss on ignition (LOI) of positive product and negative product is higher than that of the middle product for the -0.355mm size fraction, while the LOI presents gradually increasing trend from negative to positive plate for the +0.355mm size fraction. Based on the separation results and mineralogical characterizations of each size fraction of NMF, the pretreatment process including several mineral processing operations was added before triboelectric separation and better separation result was obtained.

Improving the efficiency of coal triboelectric separation by chemical conditioning

ABSTRACT A study of fine coal beneficiation in a laboratory triboelectric separation system was carried out to provide a fundamental understanding of improving the separation efficiency of thermal coal powder by chemical conditioning. Separation results of untreated and chemically treated fine coal were investigated. The experimental results demonstrated that the charge–mass ratios of clean coal and minerals increased greatly with ethanol serving as the modification chemical. The optimal deash efficiency of 85.46% was obtained when the coal was treated by 2.0 kg/t ethanol. However, excessive dosage of chemical agents had a bad effect on the separation results.

Effect of tribocharger material on the triboelectric characteristics of coal and mineral particles

ABSTRACT Dry triboelectric separation of coal depends on tribocharge difference of the coal and gangue minerals. A suitable tribocharger material which makes the coal and minerals tribocharged of opposite polarity is of great importance for triboelectric separation. In this paper, the composition of coal was analyzed by x-ray diffraction (XRD), and the triboelectric characteristics of coal and other ash-forming minerals were tested using stainless steel (SS), polyvinyl chloride (PVC), pentatricopeptide repeats (PPR), polyfluortetraethylene (PPFT), and polymethyl methacrylate (PMMA) tribochargers in lab triboelectric unit. The charge−mass ratio of coal and mineral particles were presented and evaluated. Infrared spectroscopy was adopted to analyze the different tribocharge properties between clean coal and minerals. The results show that the gangue minerals in coal are mainly pyrite, kaolin, calcite, dolomite, and quartz. The conductive mineral had the lowest chargeability, especially tribocharged with conductive material. Compared with the inorganic surface, the organic surface is easy to lose electrons and charge positively. According to the triboelectric characteristics of coal and minerals, PMMA is more suitable as tribocharger material for triboelectric separation of pulverized coal compared with PVC, PPFT, PPR, and SS. The better separation efficiency of Tai Xi anthracite coal is obtained by using PMMA tribocharger.

Recovery of valuable components from waste LCD panel through a dry physical method

A waste liquid crystal display (LCD) panel was recycled synthetically and cleanly by using dry physical methods, namely, mechanical exfoliation, dry crushing and vibrated gas-solid fluidized bed separation. Results of elemental and phase analyses show that indium and tin contents were enriched greatly in indium tin oxide concentrate obtained from colour filter and thin-film transistor glass. The results of crushing, ash content and scanning electron microscopic analyses show that when the LCD panel was crushed into particles smaller than 0.25mm, the polarizer film is nearly completely liberated from the glass. Moreover, the results of vibrated gas-solid fluidized bed separation show that gas velocity and separation time are the main factors influencing the separation. The vibration intensity of 6.8, gas velocity of 13.6cm/s and fluidizing time of 30s are the optimum operating parameters, and the degree of separation and recovery of polarizing film reached up to 37.69 and 72.3%, respectively. Based on these results, the combination of dry enrichment, dry crushing and dry separation in a flowsheet is proposed for recycling of waste LCD panel.