NL2027109B1 - Three-dimensional ecological network for soil remediation in abandoned rare earth mine area and maintenance method thereof - Google Patents

Abstract

Disclosed is a three—dimensional ecological network for soil remediation in an abandoned rare earth mine area and a maintenance method thereof, belonging to the technical field of ecological remediation of soils in mining wastelands. The ecological network is set up by digging trenches in the surface of soil (00) by manpower, orderly fixing soil fixation units (10) in the trenches, and backfilling the trenches with the soil (OO) dug out of such trenches, ensuring that 3/4 of each soil fixation unit (10) is buried in the soil (00). Each soil fixation unit (10) is set up by fixing a horizontal square frame (11) to the corresponding trench by means of a vertical wooden peg (12), and placing modified biochar (13), a carbon—fiber net membrane (14), grass seeds (15) and saw dust (16) on the horizontal square frame (11) in sequence from bottom to top. The disclosed ecological network and the maintenance method thereof may play an important role in effectively improving the ecological environment degraded extremely due to tailings wasteland in the rare earth mine area and enhancing the treatment effects on ecological destruction and environmental pollution of the mine area caused by the mining of rare earth deposits.

Description

THREE-DIMENSIONAL ECOLOGICAL NETWORK FOR SOIL REMEDIATION IN ABANDONED RARE EARTH MINE AREA AND MAINTENANCE METHOD THEREOF

TECHNICAL FIELD The present disclosure belongs to the technical field of ecological restoration of soils in abandoned mine lands, and relates to a three-dimensional ecological network for soil remediation in an abandoned rare earth mine area and a maintenance method thereof.

BACKGROUND Rare earths, also called “industrial gold”, are decisive materials in the field of high and new technology, and are listed as specified minerals and strategic resources in China. According to the white paper “Situation and Policies of China's Rare Earth Industry” released by the State Council Information Office of China in 2012, China is relatively abundant in rare earth resources with a relatively complete range of rare earth minerals. China's rare earth reserves, estimated at about 18590 thousand tons, account for approximately 23% of the world's total. The southern part of Jiangxi province possesses above 30% of China’s ion-adsorbed heavy rare earth deposits, with prospective reserves at above 9400 thousand tons and proven reserves at 468.9 thousand tons, and therefore is praised as the “rare earth kingdom” in China.

Since 1970s, three different techniques (tank leaching, heap leaching and in situ leaching) have been employed successively in the mining of ion-adsorbed rare earth ores in south Jiangxi. The three techniques have the characteristics of damaging vegetation, causing soil erosion, being low in extraction rate of rare earths and utilization ratio of rare earth resources, etc. Thousands of abandoned tailings were left behind as “southern desert” for decades on account of the mining by tank leaching and heap leaching techniques. Moreover, disorderly exploitation, extensive industrial management and severe unauthorized mining in rare earth mine areas have resulted in widespread environmental pollution and ecological damage, causing a large quantity of rare earth metals and other metals to migrate into mine soil to damage the environment with a considerable waste of rare earth mines. Besides, migration, accumulation, conversion and diffusion of such rare earth metals under combined action of natural phenomena and human activities may have influence and potential hazards on the atmosphere, plants, aquatic ecosystems and residents around the mine areas. A previous study showed that rare earths were obviously accumulated in soil within a range of 8-10 km downstream of a polluted site by rare earth mining and the soil nearest to the tailing dam had a mixed rare earth content of 27549.58 mg/kg, which was more than 160 times the average soil rare earth content in China, with a damaged rare earth mine area of 78.13 km? and a soil erosion damage area of 7.72 km},

85.85 km? in total. Rare earth ores are often associated with lots of available heavy metals. For example, rare earth ores in Bayan Obo are associated with rich Cu, Pb and Zn, and rare earth ores in Mianning county of Sichuan are rich in Pb, As and etc. The elute of weathered crust elution-deposited rare earth ores in south Jiangxi mainly contains e.g. Al*, Fe, Cd*, Pb?*, Zn?*, Mn?* and Cn”, and such heavy metals are finally present in the form of hydroxides or sulfides during the precipitation process of rare earths. It's shown that the surrounding water of a rare earth mine area in south China is heavily polluted by Pb, Cd, Cu and Zn. Rare earth mining activities in south Jiangxi severely destroyed the environment. The extensive exploitation caused great damage to vast mountains and streams, which brings much trouble to the local government and residents. Therefore, in view of the damage caused by rare earth mining to the surrounding environment, it is of great practical significance for protecting the environment and human health at the source to carry out remediation of heavy metal polluted soil in wastelands and ecological restoration of “the southern desert”. At present, few techniques are developed for soil remediation in abandoned rare earth mines for such reasons as extreme depletion, low organic matter content, low clay grain content, poor soil texture, lack of soil aggregates, poor structure and poor capability to preserve fertilizer and water of soil substrates in abandoned rare earth mine lands. Current soil remediation patents mainly involve in-situ treatment and ex-situ treatment. Concerning the in-situ treatment, for example, Chinese invention patent No. CN102640590A (Application No. 201210125698.0) disclosed a method of revegetation of rare-earth tailings with arbuscular mycorrhizal fungi, where the arbuscular mycorrhizal fungi employed were prone to symbiosis with plants and could improve the capability of plants to obtain mineral nutrients, alleviate the toxic action of rare earth elements on plants and promote the planting and growth of plants on rare-earth tailings. For the ex- situ treatment, for example, Chinese invention patent No. CN106282554A (Application No. 201610669586.X) disclosed a method of remediation of a rare earth mine, including subjecting rare earth tailings to ball mining and dressing to obtain raw tailing powder, and then acidifying, filtering, separating and backfilling the tailing powder, thus achieving a green harmless remediation effect without tailings and hidden danger left. The disclosed invention patents relating to the remediation techniques for rare earth mines simply employed microorganisms and plants without consideration of soil erosion of abandoned rare-earth mine lands.

SUMMARY An objective of the present disclosure is to overcome the defects and shortcomings inthe prior art and to provide a three-dimensional ecological network for soil remediation in an abandoned rare earth mine area and a maintenance method thereof so as to comprehensively solve the problems of soil erosion, restoration of soil properties and soil pollution treatment in the abandoned rare earth mine area.

The objective of the present disclosure is achieved as follows.

Biomass-based soil fixation materials in the form of a grillage are used to solve the problems of soil erosion, difficulty of plant survival in soil and soil pollution treatment in an abandoned rare earth mine. In other words, provided is a new idea of reducing both heavy metal pollution and ammonia nitrogen pollution of soil (a multi-part pollutant “absorption well” system is set up based on the principles of aggregation and adsorption by biochar, secondary absorption and extraction by plants, etc.). The ecological network for remediation is stable, durable, environmentally-friendly, etc., and can be regarded as a new approach to recycle crop wastes.

I. Three-Dimensional Ecological Network for soil Remediation in Abandoned Rare Earth Mine Area The ecological network includes soil 00 in which soil fixation units 10 are disposed. Corresponding trenches are dug by manpower in the surface of the soil 00. The soil fixation units 10 are orderly fixed in the trenches, and the trenches are backfilled with the soil 00 dug out of such trenches, ensuring that 3/4 of each soil fixation unit 10 is buried in the soil 00.

The soil fixation unit 10 includes a horizontal square frame 11, a vertical wooden peg 12, modified biochar 13. a carbon-fiber net membrane 14, grass seeds 15 and saw dust

16.

The horizontal square frame 11 is fixed to the trench by means of the vertical wooden peg 12.

The modified biochar 13, the carbon-fiber net membrane 14, the grass seeds 15 and the saw dust 16 are placed on the horizontal square frame 11 in sequence from bottom to top.

II. Maintenance Method

1. A particular amount of water is sprayed on the surfaces of the soil fixation units.

2. The vertical wooden pegs are kept stable and regularly inspected and fixed. The depth of the wooden peg is adjusted immediately when in a slope collapse zone to keep the ecological network stable.

3. A hollowed-out slope soil fixation zone formed after the soil is washed away therefrom is immediately filled with soil so as to underlay the zone, and the zone is moderately overlaid with soil.

4. Plant harvesting and fertilizer (phosphate fertilizer) applying are carried out regularly, and pesticides are spread to eliminate pests. The present disclosure has the following advantages and beneficial effects: 1) low fabricating cost and ease of implementation; 2) secondary utilization of resources; 3) effective prevention of soil erosion; and 4) compared with similar methods, lower cost, and good appearance, high safety, and ease of promotion and use, with promising future and enormous market demand. In summary, the present disclosure may play an important role in effectively improving the ecological environment degraded extremely due to tailings wasteland in the rare earth mine area and enhancing the treatment effects on ecological damage and environmental pollution of the mine area caused by the mining of rare earth deposits.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic structural diagram (top view) of an ecological network according to an embodiment of the present disclosure. FIG. 2 is a schematic structural diagram (three-dimensional view) of soil fixation unit 10 according to an embodiment of the present disclosure. FIG. 3 is a schematic structural diagram (top view) of horizontal square frame 11 according to an embodiment of the present disclosure. What reference numerals in the drawings denote are: 00-soil (soil in an abandoned rear earth mine area); 10-soil fixation unit; 11-horizontal square frame; 12-vertical wooden peg; 13-modified biochar; 14-carbon-fiber net membrane; 15-grass seeds; and 16-saw dust.

DETAILED DESCRIPTION Detailed descriptions will be made below in conjunction with the accompanying drawings and embodiments. I. Ecological Network 5 1. Overall Structure As shown in FIG. 1, the ecological network includes soil 00 in which soil fixation units 10 are disposed. Corresponding trenches are dug by manpower in the surface of the soil 00. The soil fixation units 10 are orderly fixed in the trenches, and the trenches are backfilled with the soil 00 dug out of such trenches, ensuring that 3/4 of each soil fixation unit 10 is buried in the soil 00.

2. Soil Fixation Unit 10 As shown in FIG. 2, the soil fixation unit 10 includes a horizontal square frame 11, a vertical wooden peg 12, modified biochar 13, a carbon-fiber net membrane 14, grass seeds 15 and saw dust 16. The horizontal square frame 11 is fixed to the trench by means of the vertical wooden peg 12. The modified biochar 13, the carbon-fiber net membrane 14, the grass seeds 15 and the saw dust 16 are placed on the horizontal square frame 11 in sequence from bottom to top. 1) Biomass-based Horizontal Square Frame 11 As shown in FIG. 3, the horizontal square frame 11 is a biomass frame formed from rice straw and corn straw having a side length of 60 cm. Waste biomass materials such as rice straw and corn straw may be reclaimed and mechanically rolled into flat straw materials, and then 1-2 cm wide flat straw materials may be picked out and woven into 8 cm wide strips. Subsequently, the strips may be connected to form the square frame having a side length of 60 cm and a width of each side of 8 cm. The horizontal square frame serves as a basic element of the ecological network to support other materials. 2) Vertical Wooden Peg 12 Several waste tree branches or wooden sticks (having a diameter of about 2 cm and a length of about 40 cm) may be collected, and a lower portion of each branch or stick may be cut into an inclined surface of about 60 degrees. The vertical wooden peg serves to fix the biomass-based horizontal square frame 11 and can be inserted into the trench easily.

3) Modified biochar 13 The modified biochar 13 is a high-quality soil conditioner, which may be a modified high-specific surface area solid material prepared by pyrolysis under a condition, for example, anaerobic.

The material serves to adsorb heavy metal and ammonia nitrogen ions, etc, in soil, buffering the acid-base environment. This material is highly potential in cation exchange, and may be used to increase the organic carbon content and the organic matter content in soil, improve the structure of soil microbial community, promote the microbial diversity, increase the biomass of plants and enhance the disease and insect resistance of plants.

4) Carbon-fiber Net Membrane 14 The carbon-fiber net membrane is a 30 to 50-mesh thin-layer carbon-fiber net.

The carbon-fiber net serves to fix the grass seeds, and adsorb heavy metals, etc.

5) Grass Seeds 15 The grass seeds 15 may be those of cogongrass (Imperata cylindrica (L.) Beauv.) and bermuda grass (Cynodon dactylon (L.) Pers.) in a ratio of 1:2, with a growing density of 80-100 plants per square meter.

Fast-growing tolerant grass seeds suitable for mountainous lands: cogongrass and bermuda grass, may be sowed in a ratio of 1:2, with a density of 80-100 plants per square meter.

The grass seeds may grow into tolerant plants for soil fixation and to extract heavy metals and ammonia-nitrogen ions aggregated in the adsorptive substrate, and thus can deeply reduce such ions.

6) Saw Dust 16 The saw dust serves as a substrate for the grass seeds to preserve moisture and fertility with good air permeability.

Claims (4)

Conclusions 1. A three-dimensional ecological network for soil remediation in an abandoned rare earth mining area, consisting of soil (00); wherein, ground fixation units (10) are placed in the ground (00); corresponding trenches are dug into the surface of the ground by manpower (00); the ground fixation units (10) are fixed in the trenches orderly and the trenches are backfilled with the soil (00) dug from such trenches so that 3/4 of each ground fixation unit (10) is buried in the ground (00 ); each ground fixation unit (10) comprises a horizontal square frame (11), a vertical wooden peg (12), modified biochar (13), a carbon fiber mesh membrane (14), grass seeds (15) and sawdust (16); the horizontal square frame (11) is fixed to the slot by means of the vertical wooden pin (12); and the modified biochar (13), the carbon fiber mesh membrane (14), the grass seeds (15) and the sawdust (16) are successively placed on the horizontal square frame (11) from bottom to top. The three-dimensional ecological network for soil remediation in an abandoned rare earth mining area according to claim 1, wherein the horizontal square frame (11) is a biomass frame formed from rice straw and corn straw having a side length of 60 cm and a width of each side of 8 cm. 3. The three-dimensional ecological network for soil remediation in a derelict area of rare earth mines according to claim 1, wherein the grass seeds are those of cogongrass (I. cylindrica (L.) Beauv.) and bermuda grass (C. dactylon (L.) Pers.) in a ratio of 1:2, with a growth density of 80-100 plants per square meter. A maintenance method based on the ecological network according to claims 1-3, comprising: 1) spraying a certain amount of water on the surfaces of the ground fixation units; 2) keeping the vertical wooden pegs stable, regularly inspecting and fixing the pegs, and immediately adjusting the depth of the wooden pegs in a collapse zone to keep the ecological network stable; 3) immediately filling, with soil, a hollowed-out slope soil fixation zone formed after the soil has been washed out therefrom, to lay the zone under, and moderately covering the zone with soil; and 4) harvesting plants and applying manure (phosphate fertilizer) regularly and spreading pesticides to eliminate pests.