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Industrial pollution in china

Par   •  22 Février 2019  •  Étude de cas  •  1 781 Mots (8 Pages)  •  87 Vues

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Outline of the problem (See appendix for the original story)  

Graphite is essential to make lithium-ion batteries used in smartphones and electric cars. Many factories producing graphite are located in China because of the low cost for production. After being produced in China, the graphite is sold to manufacturers of lithium-ion batteries such as Samsung, Panasonic and LG Chem. However, graphite factories generate pollution and this pollution affects Chinese villages around the factories. Dust from graphite is discharged in the air which can lead to respiratory problems since it is inhaled by villagers. It is also deposited on soil killing the crops and the trees and it contributes to soil contamination. In addition, dust from graphite goes into water making it undrinkable. During the production of synthetic graphite in the factories, the graphite dust released in the air contains polycyclic aromatic hydrocarbons (PAHs) because carbon precursors of synthetic graphite including coal or petroleum are heated at high temperature which releases PAHs [1,2].  

Geography of the affected region

There are three graphite plants located in villages in the Heilongjiang province in the northeastern of China. The central part of this province is the Sungari-Nen plain which is delimited by the three following mountain ranges of medium elevation: the Da Hinggan Range of Inner Mongolia on the west, the Xiao Hinggan Range on the North and the Zhangguangcai and Laoye ranges on the east [3]. The mountains of the Da Hinggan Range contain igneous rocks that are resistant to erosion [3]. The Xiao Hinggan Range is made of granite, volcanic basalt, metamorphic rocks and stratified rocks [3]. The Sungari-Nen plain contains a large amounts of bogs and swamps whereas in the western part of the plain sand dunes are present making the plain much drier in this area [3].

Soil type in the affected region

The soil type in Heilongjiang is black soil [4]. Black soil is rich in organic matter and this is why it is considered as one of the most fertile soils in China [4]. Normally under natural vegetation cover, black soil has high water content and a low temperature which promote the accumulation of organic matter [4]. However, these conditions changed over years due to farming. In fact, the soil conditions changed from humid and cool to dryer and warmer increasing the microbial activity in the soil [4]. As a result, the organic matter in the soil is decomposed faster [4]. Continued cultivation decreased the organic matter content of the soil as well as the total nitrogen content and carbon to nitrogen ratio [4]. The main result of that continuous cultivation is a reduction in fertility over time [4].

Chemistry of the pollutant

Graphite is a gray-black mineral that is only composed of carbon [5]. The carbon atoms in graphite are organized in sheets that interact together through weak Van der Waals forces whereas the carbon atoms within the sheets interact with each other through strong covalent bonds [5]. Even with strong covalent bonds, the sheets in graphite can slip over each other making graphite a soft compound [5]. Graphite is naturally occurring in metamorphic and igneous rocks [5]. Besides natural graphite, synthetic graphite also exists. This man-made form of graphite is produced in factories using carbon precursors at high temperature [1]. The precursors must contain carbon and the ones that are mostly used include petroleum and coal [1]. During the production of synthetic graphite in plants, coal or petroleum are heated at high temperature [1]. Polycyclic aromatic hydrocarbons (PAHs) are released during the combustion of coal and petroleum, so synthetic graphite production leads to the release of PAHs [2].  

PAHs are composed of two or more fused benzene rings that contain carbon and hydrogen atoms [6]. Examples of PAHs include naphthalene, phenanthrene, pyrene and benzo(a)pyrene [6]. The structure of PAHs matters because when the molecular weight increases, volatilization and solubility of the PAHs decrease whereas bioaccumulation, absorption to particles and environmental persistence increase [6]. Therefore, PAHs are persistent in the environment mainly because of their hydrophobicity and their ability to adsorb onto organic matter of solid particles, so they do not dissolve in water and they stick to organic molecules in soil [2].  As a result, air, soil, water and vegetation are the principal environmental sinks for PAHs with soil as the main one [2].

Effects of the pollutant on health

Graphite factories release graphite dust, which contains PAHs, in the air and the water. Therefore, the villagers who live around these factories breathe the polluted air. Consequently, after a long exposure to graphite dust their lungs may be affected and symptoms such as chest tightness, shortness of breath, cough, black sputum and pain may occur [7]. Ultimately, graphite dust causes pneumoconiosis [7]. Other routes of exposure are the contact of dust with the eyes and the skin [7]. In addition, PAHs can alter DNA which can lead to cancer and ultimately they can cause death [6].

Possible remediation solutions

Soil is the main place where PAHs are deposited, thus the remediation solutions have to target the soil of the affected region. Many remediation solutions are available to treat soils contaminated with PAHs. Potential solutions include solvent extraction, bioremediation, phytoremediation and chemical oxidation [2].

Solvent extraction is a process in which a solvent or mixtures of solvents are used to remove PAHs in the soil [2]. Organic solvent, surfactants, cyclodextrins and vegetable oil are examples of solvents used in the PAHs extraction procedure [2].

Bioremediation is a solution where the contaminants are broken down by aerobic or anaerobic microorganisms [2]. In the case of aerobic microorganisms, oxygen is the electron acceptor that is used by the microbes to break down organic and inorganic matters yielding carbon dioxide and water as the final products [2]. On the other hand, anaerobic microorganisms use nitrate, sulphate, iron or carbon dioxide as the electron acceptor to break down organic compounds yielding carbon dioxide and methane as the ultimate products [2].

Phytoremediation is a remediation method where plants are used to extract, sequester and detoxify pollutants, such as PAHs, present in the environment [2]. Phytoremediation is done with grass, trees or it can be combined with bioremediation techniques to enhance the removal of PAHs [2].

The last potential solution to remediate the contaminated soil with PAHs is the use of oxidation reactions [2]. Fenton’s reagent is an oxidant that can be used because it produces unstable hydroxyl radicals that have the ability to degrade organic compounds like PAHs [2].

Recommended solution

The recommended solution to remediate the contaminated soil with PAHs is solvent extraction with vegetable oil because this solvent is non-toxic, cost-effective and biodegradable [2]. Vegetable oil is hydrophobic, so it is a sorption medium for hydrophobic molecules like PAHs [2]. Sunflower oil has been shown to remove more PAHs when soil moisture is low, which is the case in Heilongjiang province where the soil is dry due to continued soil cultivation [2, 4].         A removal of 81-100% of PAHs in contaminated soil was obtained in experiments with sunflower oil [2]. Therefore, sunflower oil should be used to remediate PAHs in the soil of Heilongjiang. The soil: oil ratio that should be used to attain this high efficiency is 1kg of soil: 4L of sunflower oil [2].

To test this solution, I would perform a column solubilisation experiment [8]. To do this experiment, a sample of contaminated soil taken from the region of Heilongjiang has to be packed into a column and then sunflower oil will be added in the column [8]. The oil will pass through the soil and be collected at the bottom of the column [8]. The amount of PAHs in the sunflower oil will be measured and it will be expected that PAHs be solubilized by sunflower oil [8]. Some of the oil will remain in the soil, but it will be degraded if adequate air exchange and nutrient supply are maintained in the soil [8].

Appendix

Below is a part of the article called “In your phone, in their air” by Peter Whoriskey (Full story at https://www.washingtonpost.com/graphics/business/batteries/graphite-mining-pollution-in-china/)  

At night, the pollution around the village has an otherworldly, almost fairy-tale quality. “The air sparkles,” said Zhang Tuling, a farmer in a village in far northeastern China. “When any bit of light hits the particles, they shine.” By daylight, the particles are visible as a lustrous gray dust that settles on everything. It stunts the crops it blankets, begrimes laundry hung outside to dry and leaves grit on food. The village’s well water has become undrinkable, too. Beside the family home is a plot that once grew saplings, but the trees died once the factory began operating, said Zhang’s husband, Yu Yuan. “This is what we live with,” Zhang said, slowly waving an arm at the stumps.

Zhang and Yu live near a factory that produces graphite, a glittery substance that, while best known for filling pencils, has become an indispensable resource in the new millennium. It is an ingredient in lithium-ion batteries. Smaller and more powerful than their predecessors, lithium batteries power smartphones and laptop computers and appear destined to become even more essential as companies make much larger ones to power electric cars. The companies making those products promote the bright futuristic possibilities of the “clean” technology. But virtually all such batteries use graphite, and its cheap production in China, often under lax environmental controls, produces old-fashioned industrial pollution.

At five towns in two provinces of China, Washington Post journalists heard the same story from villagers living near graphite companies: sparkling night air, damaged crops, homes and belongings covered in soot, polluted drinking water — and government officials inclined to look the other way to benefit a major employer.

References

[1] Tamashausky, A. V. (2006). An Introduction to Synthetic Graphite. Retrieved November 9, 2016 from https://asbury.com/pdf/SyntheticGraphitePartI.pdf 

[2] Gan, S., Lau, E. V., & Ng, H. K. (2009). Remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Journal of Hazardous Materials, 172(2-3), 532-549. doi:10.1016/j.jhazmat.2009.07.118 

 [3] Falkenheim, V. C. (2013, March 27). Heilongjiang. Retrieved November 9, 2016, from https://www.britannica.com/place/Heilongjiang

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