Treatment of Heavy Metal Pollution in Sediment and Its Resource Utilization in Building Ceramics

Chenhao LIANG, Lidan CAI, Zhuoxu NIE, Xinhao ZHAO, Chen WANG*, Xiaohong XIONG

1. College of Urban Construction, Jiangxi University of Technology, Nanchang 330022, China; 2. College of Business, Nanchang Jiaotong Institute, Nanchang 330022, China

Abstract With the rapid development of China’s social economy and the acceleration of urbanization, a large quantity of production and domestic sewage is discharged into rivers and lakes, and the concentration of pollutants leads to serious excessive heavy metals in sediment, which affects the ecological environment. In this paper, the treatment technology of heavy metal pollution in sediment and its resource utilization in building ceramics in China are systematically analyzed and summarized, in order to provide a reference for the treatment of sediment in rivers and lakes and the sustainable development of building ceramics industry.

Key words Sediment, Building ceramics, Resource utilization, Research progress

1 Introduction

In recent years, with the rapid development of social economy and the acceleration of urbanization in China, a large quantity of polluted industrial wastewater and domestic sewage has been discharged into rivers and lakes, resulting in serious pollution of water environment, while a large number of pollutants in water gather in sediment, resulting in serious over-standard heavy metal content in sediment, and the polluted sediment will cause secondary pollution of water body due to the change in environmental conditions, thus destroying water ecological environment.

At present, with the continuous advancement of urbanization in China, the market demand for building ceramics is increasing day by day. With the continuous mining of existing kaolin, natural mud and other raw materials, regional environmental pollution is caused, especially the mining of kaolin tailings has caused environmental pollution and a large number of potential safety hazards[1]. Against this background, the resource utilization of sediment in building ceramics has attracted wide attention of scholars at home and abroad. The resource utilization of sediment in building ceramics can not only realize the treatment of heavy metal pollution in sediment and the protection of water ecological environment, but also effectively reduce the demand for natural resources in building ceramics industry and alleviate the environmental pollution problems caused by resource exploitation, which is of great significance to the protection of water ecological environment and the sustainable development of building ceramics industry[2].

2 Research progress of heavy metal pollution in sediment and its treatment technology

2.1CurrentsituationofheavymetalpollutioninsedimentinChinaIn recent years, many domestic scholars have studied and analyzed the current situation of heavy metal pollution in sediment of important reservoirs or rivers and lakes, and it is generally found that the heavy metal contents in sediment of reservoirs obviously exceed the standard, especially in reservoirs seriously affected by industrial sewage. The research of Fan Chengxinetal.found that Cd pollution in lake and reservoir sediments in China was the most serious, and it even reached moderate or severe pollution level[3]. In the sampling investigation of a reservoir in Guangdong, Linyi Reservoir and 132 large and medium-sized reservoirs in Ganjiang River Basin, it was found that there was a risk of heavy metal pollution in reservoir sediment, and Cd, Mn, Cu and so on exceed the standard, posing a certain threat to human life and the survival of animals and plants[4-6]. Therefore, it is extremely urgent to control the heavy metal pollution in sediment, and it is of great significance to realize the resource utilization of sediment.

2.2MaintechnologiesfortreatmentofheavymetalpollutioninsedimentAccording to the remediation theory of heavy metal pollution in sediment, the existing sediment treatment technologies can be roughly divided into two categories according to the remediation location:in-situremediation andex-situremediation.In-situremediation is a technology that directly adopts comprehensive means to treat sediment without moving it;ex-situremediation is a technology of transporting polluted sediment from river channel and then treating it. In practice,ex-situremediation has the characteristics of high input cost, soin-situremediation is more widely used.

2.2.1In-situremediation technology.In-situremediation technology refers to the treatment of sediment directly in contaminated sites to reduce the pollution of sediment to water, and it can be divided intoin-situphysical remediation technology,in-situchemical remediation technology andin-situbioremediation technology.

(i)In-situphysical remediation technology. At present, the commonin-situphysical remediation technologies mainly include capping remediation technology and electric remediation technology. Capping remediation technology uses covering materials to separate sediment from the water above, so as to inhibit the release of heavy metals from sediment to water[7], but it will reduce the water depth and water capacity of reservoirs, rivers and lakes. Electric remediation technology is a fast and efficientin-situgreen remediation technology. By putting sediment pollutants into an electrolysis device with cathode and anode, a series of electrochemical reactions are carried out by using electric field, and then the electrodeposition or ion exchange extraction of heavy metal ions or compounds in the electrode area is realized, so as to achieve the effect of removing heavy metals from sediment, and it has a good application prospect[8]. (ii)In-situchemical remediation technology.In-situchemical remediation technology uses chemical reagents to react with the sediment at the bottom of the river to separate, fix pollutants in the sediment or transform them into non-toxic chemical forms, thus reducing the diffusion and migration ability and toxicity of heavy metals in the sediment[9]. At present, the reagents with good remediation effect used in this technology mainly include calcium polysulfide, ferrous sulfate, sodium dithionite,etc.[10], but the dosage of reagents should be carefully treated in practical application to avoid the potential harm of inappropriate reagents or dosage to regional water ecological environment, which makes thein-situchemical remediation technology have certain limitations. (iii)In-situbioremediation technology.In-situbioremediation technology refers to the purification of heavy metal pollutants in sediment by microbial reagents or aquatic animals and plants under certain conditions. Thein-situbioremediation technology has the advantages of convenient operation, low price and little environmental interference. However, whether it is animal, plant or microorganism, as long as it exceeds the maximum tolerance of heavy metals, the effect of ecological restoration will be reduced, and even there will be counterproductive effect[11].

2.2.2Ex-situremediation technology. Theex-situremediation technology refers to the removal of sediment pollutants from the original positions in rivers or lakes and reservoirs, and it can be divided into on-site remediation and off-site remediation. Compared within-situremediation technology, this technology has certain operability and controllability in engineering, and has certain advantages for small polluted areas, but it may cause secondary environmental pollution in the remediation process[10]. At present,ex-situremediation technology has been applied in many engineering cases at home and abroad, which provides experience for the combination ofex-situremediation technology and other technologies.

3 Progress in resource utilization of sediment in building ceramics

At present, the ceramic industry consumes an average of 2.8 billion t of raw materials and 48.7 million t of coal for production every year[12]. This large amount of energy consumption is obviously contrary to the concept of ecological civilization construction and sustainable development in China. The composition of sediment is the same as that of clay, and it can replace clay to produce ceramic, ceramsite and other materials, and its resource utilization can boost the sustainable development of the ceramic industry. For this reason, local governments in China have successively issued relevant policies to support the reform and development of this industry. For example, the 13thFive-YearDevelopmentPlanofNewWallMaterialsinZhejiangProvinceissued in 2016 clearly pointed out that it is necessary to adhere to green development and actively carry out demonstration and promotion of silt resource utilization. Since the release of the plan, some enterprises in Zhejiang Province have successfully realized large-scale utilization of silt resource utilization[13]. At the same time, many scholars in China have also carried out research on the resource utilization of sediment in building ceramics and achieved rich results. For example, Mao Ruietal.found that a certain amount of dredged silt in combination with natural clay was used to prepare building ceramics, the proportion of dredged silt used was as high as 20%, which realized the reuse of resources and considerable economic benefits[14]. The research of Xiao Jiboetal.showed that high-efficiency phosphorus-removing sediment ceramsite could be obtained under certain conditions by mixing river sediment with pore-forming agentCyperusinvolucratusRottboll, coal granules, cement and water. The prepared sediment ceramsite not only had certain phosphorus removal ability, but also effectively reduced the required cost, so it was one of the suitable sediment resource utilization schemes[15].

4 Conclusion

(i) The internal components of sediment pollutants are complex, and may cause secondary pollution to the water ecological environment in the treatment process. Therefore, it is necessary to comprehensively utilize a number of technical means to reduce the potential risks of sediment pollution treatment. (ii) To build a beautiful and livable ecological environment and realize sustainable development, dredging and resource utilization of river and lake sediment is one of the important ways. To realize resource utilization of sediment, it is necessary to promote resource utilization of sediment in building ceramics on the basis of sediment pollution control, combined with sediment characteristics and siltation trend. (iii) The resource utilization of sediment in building ceramics needs the support of building ceramics enterprises, and the development of building ceramics enterprises can not be separated from local policy support. Local government departments need to strengthen their support to building ceramics enterprises, especially to increase the policy support to resource utilization of sediment in building ceramics.