Optimization of the recovery of plastics for recycling by density media separation cyclones

Material recovery processes are presented as the optimum option for recycling plastic wastes as a means of recovering hydrocarbon resources. There exist a large variety of automated material recovery processes for recycling of such wastes but each with significant limitations. Of these, the separation based on differences in densities is advocated as the optimum process either for producing recycled products or preparing wastes for subsequent recovery processing.Density separation processes based on cyclone type density media separation (DMS) is presented as an important, potential method for increasing plastics recycling process capacities. It is demonstrated to have the capacity to separate a significantly larger range of particle sizes than those presently processed industrially. The mathematical relationship for the prediction of quality of typical LARCODEMS type density media separations by particle size and density as expressed by the Ecart Probable is presented.A proposed device configuration is presented for density media separation to optimize the recovery and purity of both density fractions produced. It is also suggested that to be economically viable, a large scale of operation is required for industrial plastics recycling operations recovering and producing a number of different plastics with a purity to be used as a substitute for virgin material.     

Chlorobenzenes and organochlorinated pesticides in vegetable soils from an industrial site, China

Organochlorinated compounds are ubiquitous contaminants in the environment, especially in industrial sites. The objective of the work was to investigate whether a vegetable field near an industrial site is safe for vegetable production. The residues of chlorobenzenes (CBs), hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in a vegetable field which was near a chemical plant in China were characterized. Point estimate quotient was used for ecological risk assessment of the investigated site. The results showed that all CBs except monochlorobenzene (MCB) were detected in soils. The total concentrations of ∑CBs ranged from 71.06 to 716.57 ng/g, with a mean concentration of 434.93 ng/g. The main components of CBs in soil samples were dichlorobenzenes (DCBs), trichlorobenzenes (TCBs) and tetrachlorobenzenes (TeCBs), while for single congeners, 1,2,4-TCB had the highest concentration, which ranged from 13.21 to 210.35 ng/g with a mean concentration of 111.89 ng/g. Residues of hexachlorobenzene (HCB) in soil samples ranged from 0.9 to 11.79 ng/g, significantly lower than ∑DCB, ∑TCB and ∑TeCB. Concentrations of ∑HCHs and ∑DDTs in soils ranged from 11.32 to 55.24 ng/g and from 195.63 to 465.58 ng/g, respectively, of which the main components were αup-HCH and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE). Ecological risk assessment for the investigated site showed that the most potential risks were from TCBs and TeCBs, based on the hazard quotients. The higher residues of CBs and DDTs compared to the target values and the higher than 1 hazard quotients indicated that this area is not safe for vegetable production and thus soil remediation is needed.     

河西走廊及兰州地区典型有机氯农药的大气残留及时空分布特征

利用PUF大气被动采样器对河西走廊及兰州地区进行了为期1 a,分4个季度的大气样品采集,应用HP6890ⅡGC-ECD对大气中典型有机氯农药六六六(HCHs)和滴滴涕(DDTs)的含量进行了分析.研究结果表明,河西走廊和兰州地区大气中ΣHCHs(α-HCH+β-HCH+γ-HCH+δ-HCH)和ΣDDTs(p,p’-DDT+o,p’-DDT+p,p’-DDE+p,p’-DDD)的平均浓度分别为86.22 pg.m-3和34.06 pg.m-3,研究区ΣHCHs和ΣDDTs的背景浓度平均为54.41 pg.m-3和21.56 pg.m-3,同国内外其它地区相比,污染处于相对较低的水平.总体而言,ΣHCHs和ΣDDTs均表现出秋季浓度相对较高(均值分别为127.4pg.m-3和47.06 pg.m-3)的季节特征,酒泉、安西、张掖三地的HCHs和DDTs污染水平较高,推测与这3个地区的耕地面积和历史使用量较大有关.源解析表明,研究区内的HCHs主要来源于禁用前的历史残留以及林丹的使用,DDTs来源于工业DDTs的近期使用,部分地区如酒泉和安西可能存在三氯杀螨醇的使用.河西走廊和兰州地区人群通过呼吸途径对HCHs和DDTs的暴露水平较低.     

水库淹没带土壤有机氯农药分布特征及风险评价

采用GC-MS气相色谱与质谱联用仪,分析了密云水库南水北调来水前高程130～150 m之间的淹没带表层土壤样品中17种有机氯农药(OCPs)的含量、残留特征,讨论了有机氯农药的可能来源,并对OCPs的潜在风险进行了评价.结果表明:①密云水库淹没带土壤有机氯农药残留以六六六(HCHs)和滴滴涕(DDTs)为主,含量均值分别为1. 74 ng·g-1和1. 01ng·g-1,与国内其他湖库区相比,ΣHCHs含量相近,ΣDDTs含量较低.②水库淹没带土壤有机氯农药残留具有一定的空间分布特征.水陆域交错处土壤OCPs含量普遍高于水域、陆域土壤中含量,且存在显著性差异性.水库东部及潮河入库区、独立小流域淹没区,OCPs残留以DDTs为主;库北山前平原淹没带及库西中部淹没区OCPs则以γ-HCH残留为主;白河入库处河滩淹没区HCHs及DDTs残留均有较高占比,这与其污染来源有关.③源解析结果表明,淹没带土壤HCHs来源主要与林丹类农药的输入有关,而DDTs主要来自于早期农药使用的残留.④生态风险评价表明,水库淹没带土壤中大部分样点OCPs生态风险低,白河入库区及库西中部淹没带滴滴涕有潜在风险性.