Sharif Digital Repository

Abstract: The waste stream of electrical and electronic equipment is three times faster than other municipal waste streams. Recycling of electronic waste is necessary for both reducing environmental pollution and saving natural ores. Bioleaching is known as an efficient technology for metal leaching. In most of the previous studies on the bioleaching of electronic waste, the pH of the process was adjusted daily under the optimal pH of the bacterium growth. Using acid causes increasing process costs and unsustainability of the process. In this work, the effect of daily pH adjustment on the bioleaching efficiency of electronic waste using adapted Acidithiobacillus ferrooxidans was studied.... 

In this paper, we analyze the Internet traffic from a different point of view based on Benford's law, an empirical law that describes the distribution of leading digits in a collection of numbers met in naturally occurring phenomena. We claim that Benford's law holds for the inter-arrival times of TCP flows in case of normal traffic. Consequently, any type of anomalies affecting TCP flows, including intentional intrusions or unintended faults and network failures in general, can be detected by investigating the first-digit distributions of the inter-arrival times of TCP SYN packets. In this paper we apply our findings to the detection of intentional attacks, and leave other types of... 

SUMMARY: In this paper, we study the effects of anomalies on the distribution of TCP flow interarrival time process. We show empirically that despite the variety of data networks in size, number of users, applications, and load, the interarrival times of normal flows comply with the Weibull distribution, whereas specific irregularities (anomalies) causes deviations from the distribution. We first estimate the scale and shape parameters and then check the discrepancy of the data from a Weibull distribution with the estimated parameters. We also utilize the Weibull counting model to recheck the conformance of small flow interarrival times with the distribution. We perform our experiments on a... 

In this paper, we study the effects of anomalies on the distribution of TCP flow interarrival time process. We show empirically that despite the variety of data networks in size, number of users, applications, and load, the interarrival times of normal flows comply with the Weibull distribution, whereas specific irregularities (anomalies) causes deviations from the distribution. We first estimate the scale and shape parameters and then check the discrepancy of the data from a Weibull distribution with the estimated parameters. We also utilize the Weibull counting model to recheck the conformance of small flow interarrival times with the distribution. We perform our experiments on a diverse... 

E-waste has become one of the greatest sources of environmental pollution. Bioleaching is known as a new, simple, and environmentally friendly technology for metal recovery requiring low energy input, unskilled labor operations, moderate conditions, and low costs. Acidithiobacillus ferrooxidans is a famous and puissant mesophilic bacterium applied extensively to recover metals from ores and different industrial and municipal wastes. It is necessary to identify the parameters affecting consumers E-waste recycling. Separating and recovering different types of E-waste is impossible for small recycling units. There should be a specific combination of E-waste, enabling the extraction of the... 

There is a substantial volume of mobile phone waste every year. Due to the disadvantages of traditional methods, it is necessary to look for biological processes that are more eco-friendly and economical to recover metals from e-waste. Fungi provide large amounts of organic acids and dissolve metals but using sucrose in the medium is not economical. In this paper, the main objective is to find a suitable alternative carbon substrate instead of sucrose for fungi bioleaching of Ni and Cu in printed circuit boards (PCBs) of mobile phones using Penicillium simplicissimum. Four kinds of carbon sources (including sucrose, cheese whey, sugar, and sugar cane molasses) were selected. Also, pH and... 

In this article, bioleaching of computer printed circuit boards (CPCBs) was examined using Aspergillus niger with one-step, two-step, and spent-medium bioleaching methods. Four effective parameters were optimized using response surface methodology (RSM) to achieve maximum recovery of Cu and Ni. Under optimal conditions – pH of 5.15, pulp density of 10 g/l, 1E+007 spores of A.niger, and 4.5 days for the sample adding time − 97% and 74% of Cu and Ni were recovered, respectively. Two-step bioleaching and spent medium bioleaching were respectively identified as the best methods for maximizing Cu and Ni recovery. Fungi deteriorate the sample mainly by it is chemical action like producing acids.... 

Knowing the metal content of electronic waste is essential to evaluate metal recovery. Lack of a standard method for digestion of precious metals from electronic waste has resulted in difficulty in comparison to the efficiency of recovery. In this study, different precious metal digestion methods and economic value of precious metals from different types of waste printed circuit boards in different fraction sizes, including computer printed circuit boards, mobile phone printed circuit boards, television printed circuit boards, fax machine printed circuit boards, copy machine printed circuit boards, and central processing unit were examined. The optimal digestion method using aqua regia,... 

This research aims to expand the body of information that researchers require before starting electronic waste (E-waste) recovery experiments. With this purpose, the basic metal contents, alkalinity, polymer components, iron magnetic separation, metal recovery priority and economic values of different types of waste printed circuit boards (PCBs) were investigated. The selected wastes were computer PCBs (CPCBs), CPCBs with wires, mobile phone PCBs (MPPCBs), television PCBs (TVPCBs), fax machine PCBs (FPCBs), copy machine PCBs (COPCBs) and central processing units (CPUs). These E-wastes were prepared in the three fraction sizes of F1<1 mm, 1 < F2<3 mm, and 3 < F3<8 mm to evaluate the metal... 

Polystyrene, acrylonitrile butadiene styrene, and polypropylene are the main polymers in E-waste, existing about 31%, 16%, and 13%, respectively. In this research, the effects of the elimination of low-density materials (such as polymers and plastics) were studied using the shaking table method. Bioleaching of Cu and Ni against the original sample (Sample #1) and pre-treated sample without low-density materials (Sample #2) was compared. The amount of bioleached metals and growth characteristics (including pH, Eh, bacterial count) was investigated within 25 days. The analysis of Sample #1 showed that at pulp density of 15 g/l, 94% and 79% of Cu and Ni were recovered maximally, respectively,... 

The high amount of base metals poses an important challenge in gold bioleaching from spent printed circuit boards (PCBs). This study aims to investigate the bioleaching of important base metals (Cu, Ni, and Fe) from a mixture of spent PCBs (E-waste) using adapted Acidithiobacillus ferrooxidans in the bubble column bioreactors. Firstly, the adaptation process is done from 1 to 15 g/L in Erlenmeyer flasks in 187 days, then the concentration of E-waste increased to 40 g/L in bubble column bioreactors in 44 days. The concurrent recovery of copper, nickel, and iron using adapted bacterium in a bioreactor was optimized by central composite design. Various effective parameters such as aeration... 

The inhibition effects of 3.5 bis (2-pyridil) 4-amino 1,2,4 triazole (NBTA) and 1-10 phenantrolin (PHEN), on corrosion of mild steel in acid solutions, (sulphuric acid and hydrochloric acid) were studied. The Tafel polarisation and ac impedance techniques were employed. Results obtained reveal that both compounds are relatively good inhibitors. The inhibition efficiencies of NBTA are higher in hydrochloric acid than in sulphuric acid. This has been attributed to the synergistic effect of chloride ions present in hydrochloric acid. The mechanism of inhibition of PHEN is believed to be owing to the formation of insoluble chelates between the organic molecules and atom/ion on the metal surface.... 

In this research, Zn, Ni, and Cu recovery from mobile phone printed circuit boards was investigated. The initial pH and pulp density using Aspergillus niger or Penicillium simplicissimum fungi were optimized to improve the recovery of Zn, Ni, and Cu using a central composite design. Fungi were able to recover 97% of Cu. Often for Ni recovery, A. niger was more effective, but in low pulp densities and low pH, P. simplicissimum was preferred. For recovery of Zn, A. niger is more appropriate at pH lower than 6, but P. simplicissimum outperforms at pH higher than 6. Under the optimum conditions (pulp density of 4 gL−1 and initial pH 10), the respective recovery of Cu, Ni, and Zn was determined... 

The interaction energies of 3,5 di-methyl pyridine (A) and 2,4 di-methyl pyridine (B) on the (100) surface of body-centered cubic (bcc) iron were determined via a cluster model and ab initio quantum chemical calculations at density functional theory level. The obtained energies were used to compare the inhibition behavior of these molecules for iron corrosion in hydrochloric acid solution. The iron surface and its adsorption sites (on-top, bridge, hollow) were considered as some clusters taken from two-layered 〈100〉 planes, i.e. Fe1(1), Fe4(2,2), and Fe5(4,1). So, the process for which quantum chemical calculations was carried out consists of adsorption of molecule A (B) on these clusters.... 

In this research, Zn, Ni, and Cu recovery from mobile phone printed circuit boards was investigated. The initial pH and pulp density using Aspergillus niger or Penicillium simplicissimum fungi were optimized to improve the recovery of Zn, Ni, and Cu using a central composite design. Fungi were able to recover 97% of Cu. Often for Ni recovery, A. niger was more effective, but in low pulp densities and low pH, P. simplicissimum was preferred. For recovery of Zn, A. niger is more appropriate at pH lower than 6, but P. simplicissimum outperforms at pH higher than 6. Under the optimum conditions (pulp density of 4 gL−1 and initial pH 10), the respective recovery of Cu, Ni, and Zn was determined... 

The inhibition effects of sodium dodecylbenzenesulphonate (SDBS) and hexamethylenetetramine (HA) on the corrosion of mild steel in sulphuric acid solution have been studied using weight loss, electrochemical impedance and Tafel polarisation measurements. For HA, a monotonous increase in inhibition efficiency is observed as a function of concentration. For SDBS, however, an optimum in the inhibition efficiency is observed for a concentration close to 250 ppm, which is ascribed to the formation of hemi-micellar aggregates that provoke inhibitor desorption from the metal/solution interface at higher concentrations. Upon mixing HA and SDBS, concentration regions showing synergistic and...