Theory and practice in cemented filling with unclassified tailings structure fluid

Tom 24 2008 Zeszyt 4/3

WANG FANG-HAN*, CAO WEI-QIN*, YAO ZHONG-LIANG**

Theory and practice in cemented filling with unclassified tailings structure fluid

1. Status quo and review of unclassified tailings filling in china and other countries

Tailings from ore mill are always the first kind of material used for mine filling. Using tailings for filling underground not only increases ore recovery, prevents upper strata from collapsing and ground surface from subsiding so as to protect ground surface in mining area, but also can reduce tailings occupation land considerably and eliminate unsafe factors from tailings reservoir. One of filling modes used widely in China and other countries is classified tailings filling, i.e. tailings from ore mill, called as total tailings or unclassified tailings also, are classified, in which rough tailings are used in underground filling, and finer tailings are discharged into tailings reservoir. This kind of filling mode can make permeability coefficient of fill satisfy the technical requirements, but no use of fine tailings is made, piling of fine tailings is difficult and the requirement for construction of tailings reservoir is strict, as well as under condition of low utilization of tailings in filling or small size of ore grinding, replenishment with other materials such as river sand, grit, rod mill sand and gobi desert aggregates etc is needed.

In unclassified tailings filling, unclassified tailings are not classified and they can directly be filled underground, so that the problems above, caused by classifying of tailings, can be avoided. In high-grade iron mine where tailings output is higher and lead-zinc mine where poly-metal paragenesis occurred etc, tailings from ore mill can be totally filled underground. So, tailings reservoir can be eliminated and “zero discharge” of tailings and wastes can come true. High quality of filling with unclassified tailings can provide a good

** Nanjing Yinmao Zinc-Lead Mines Co. Ltd. Nanjing 210033, Jiangsu, China.

** Changsha Institute of Mining Research, Changsha, Hunan 410012, China.

condition for mining production, and protect effectively ground surface in mining area and surrounding environment so that total tech-economic benefits for mine are high and social environment benefit is good as well as mine.

Due to fine particles containing in unclassified tailings, the technical requirements are higher in comparison with classified tailings filling. An outstanding feature is that concentration of fill slurry must be increased. Otherwise, after fill slurry is filled into mined-out area, fine tailings will suspend on the fillbody surface and consolidation is lower.

Permeability of fillbody is poor, and dewatering of fill slurry is difficult. If overflow dewaters, a large number of fine particles and cement will rush into and pollute underground drift. Segregation of fill slurry lowers quality of filling and provides difficulty for mining production. According to this, in the case that filling with unclassified tailings is used, tailings must reach to a higher concentration so as to avoid segregation and loss of fill slurry.

In order to increase concentration of unclassified tailings slurry, many studies on it were performed in China and other countries. Currently, a filling technology used widely is that tailings are thickened and filtered as well as dewatered in two stages so as to reduce water content of filter cakes of unclassified tailings to 10%~12% or more. After metering, filter cakes of unclassified tailings are fed into agitator. After cement, other fill aggregates and water for concentration adjustment are added to agitator; these materials will be agitated into paste fill, and then pressurized by hydraulic double-cylinder piston pump or delivered, by means of natural head, to underground via filling hole and underground pipe network.

2. Definition and features of cemented filling with unclassified tailings structure fluid

Cemented filling with unclassified tailings structure fluid means that unclassified tailings from ore mill are used as aggregates in filling, cement or cement alternatives are used as cementing agent, and -20 mm particles containing in fill are not less than 15~20%. In addition, slump of fill slurry is 23~25 cm and fill slurry can flow in pipe and stope.

Meanwhile, fill slurry in empty space of stope can not segregate and dewater, flatness of slurry flow is desirable, and angle of rest is less than 3–5°C. After consolidating and hardening, completeness and homogeneity of fillbody are good, and strength of fillbody satisfies that of filling required by mining method.

According to definition above, it can be known that cemented filling with unclassified tailings structure fluid is characterized by follows:

1) Fill making up unclassified tailings and cementing agent contained 15~20% very fine particles (-20mm). In the process of piping, very fine particles, by the action of pressure, tended to flow to and formed into a lubricating layer on walls of pipe. So, on one hand, wearing of pipe wall was reduced; one the other hand, drag in piping can be decreased also. This provides condition for smooth piping of slurry.

2) Slump of fill slurry was 23~25 cm. Generally, slump was assumed to be 15~23 cm. Based on lab experiment and theoretical analysis, it was shown that flowing drag of fill slurry

was higher on condition that slump was less than 22 cm. Under the condition of smaller pipeline length – height ratio (<2~3), it was difficult to achieve flow gravity transportation and pumping transportation was necessary. Due to small slump and complicated thickening – filtering – metered feeding process for fill constituents (especially, unclassified tailings), preparation for fill was more difficult. Increasing fill slump can simplify preparation and transportation of fill slurry process so as to perform filling easily.

3) Fill slurry in pipeline and stope was in the form of structure flow. There was not velocity gradient between rough and fine particles in the process of flowing of fill slurry in pipeline and stope, but complete structure flow appeared. On condition that slump of fill slurry was less than 25 cm, slurry itself had initial shearingt0. Due to existence oft0, a low-velocity full pipe flowing of fill slurry can be achieved. Meanwhile, any segregation can not occur in a period of slurry still, and slurry can restart flowing without any plugging in a short time of slurry still. This differs in two-phase flow piping of classified tailings fill slurry substantially.

4) Segregation and dewatering of fill slurry can not occur in stope. Fill slurry with structure flow behavior can not dewater by itself. In addition, a low-velocity flowing piping can be achieved. Prior to filling, no conduction water for pipeline was needed but a little water for pipeline lubrication was used only. After filling was finished, only 2~3 m³water was used for pipeline flushing so as to reduce an effect of water to a minimal extent. In the whole process of filling, no segregation and dewatering of fill slurry in stope occurred.

A little decant water and flushing water were absorbed by fillbody itself and permeated through fissures on host rock in stope, without any catchments in stope and even overflow. So, conditions of operating in stope and underground drift were improved.

5) Good flatness of fillbody. Due to good flowing flatness of fill slurry and <3~5°C angle of rest, flatness was good after fill slurry was consolidated. Thus, on one hand, conditions of operating in stope were improved considerably. On the other hand, it was beneficial to filling in a long strip of stope and even to filling close to roof in empty space in all types f stopes.

6) Good completeness of fillbody and high quality of filling. Owing to being a structure flow of fill slurry in stope and no segregating and bedding, completeness of fillbody was good, fillbody was homogeneous and a different strength of fillbody can be obtained by means of adjusting cement – tailings ratio so that technical requirements for various mining methods or filled locations were satisfied.

3. Lab experiment for cemented filling with unclassified tailings structure fluid

In order to make cemented filling with unclassified tailings structure fluid come true, it was necessary to make a more systematic lab experiment and pilot test. According to mining method based on mining conditions of orebody, a fair strength of fillbody was determined.

According to occurrence features of orebody, a network of filling pipeline was arranged.

Based on lab experiment and pilot tests, such fair parameters as concentration, cement – tailings ratio and flow rate etc for fill slurry preparation can be determined. According to determination of rheology parameters and analysis / calculation of transportation, a method for transportation of fill slurry, i.e. gravity flow or pumped transportation, was determined.

Detailed experimental study is as follows:

1) Determination of unclassified tailings sizes and basic physical-chemical parameters Due to different properties of ore in all metal mines, difference in ore processing conditions was greater so that difference in grading of unclassified tailings, basic physical parameters (specific gravity, volumetric weight and porosity etc) and chemical performance (chemical constituent, mineral composition, useful constituent content and so on) was greater also. In the case of different concentration, different unclassified tailings slurry performed as a different state of flowing. On conditions that content of –20mm particles in unclassified tailings was higher and their specific gravity was lower, a maximal concentration of fill slurry was possibly lower than 70%. In the case of rougher unclassified tailings particles and higher specific gravity, a maximal concentration can be up to 76~78%.

2) Test for grading ratio optimization of fill slurry

According to internal and external technical conditions of mine, fill composition was selected and made a strength test under the conditions of different concentration and cement – tailings ratio, and laws of change in fillbody strength were derived. According to requirements for mining method, fair cement – tailings ratio was determined.

3) Determination of rheology parameter of fill slurry and analysis/calculation of transpor- tation performance

Slump test and flowability test (L-type pipeline test) for unclassified tailings slurry were made. On condition that provisions were provided, a cyclic pipe pumping test can be carried out to derive rheology parameter of fill slurry with various concentrations. Thus, flowing drag in various diameter pipeline, at the time of analysis and calculation of different flow rates, provided basis for design of fill pipeline network and determination of slurry transportation method (gravity flow or pumping) in mines.

4. Rheology parameter determinations and transportation performance of unclassified tailings structure fluid

Unclassified tailings structure fluid was characterized by Bingham fluid and its rheology parameter is to decide focal parameter of transportation performance, which can be ex- pressed as yield shearing stresst0and viscosity coefficiencyh. Physical significance of t0is resistance of slurry to shearing deformation in the state of still, and viscosity coefficiencyh is resistance of slurry to shearing deformation in the state of movement.t0andh0can be determined by all kinds of viscosity meters or pumped cyclic pipe test. In lab, L-type pipe gravity flow transportation test can be used to determine them, shown in Photo 1.

This device can determine flow rate and flow velocity of fill slurry prepared at different concentrations and ratios, including height of slurry column in a vertical pipe in the state of still after flow is completed. t0andh0 can be calculated by Equation (1).

t₀ ^{0 0}

4 0

= × × + r h D

h L

( )

(1)

h=(3t-4t ) 24

0 D0

V

(2)

in which:

r – volumetric weight of slurry [kN/m³],

h0 – height of slurry in vertical pipe in the state of still [m], D0– diameter of test pipe [m],

L – horizontal length of test pipe [m], V – flow velocity of slurry in test pipe [s/m],

t0 – shearing stress calculated under condition of test [Pa].

In the process of mining production, flow drag of slurryi [Pa/m] can be calculated by Equation (3):

Phot. 1. L-type pipe gravity flow transportation test device in lab

Fot. 1. Urz¹dzenie do prób przesy³u grawitacyjnego rurami L w warunkach laboratoryjnych

i D

V

=16 + D 3

0 32

2

t h (3)

in which:

i – flow drag of slurry in vertical pipe [MPa/m],

V – flow velocity of slurry in fill pipe in the case of mining production [s/m], D – inside diameter of fill pipe [m].

Sum of local drag loss and outlet loss in real filling was assumed to be 15% of drag along pipeline, the maximal pipeline length – height ratio for gravity flow transportation was derived from Equation (4).

N H L H

r

= + - i 115.

(4)

in which:

H – sum of vertical pipe heights of fill pipe network [m], L – sum of horizontal lengths of fill pipe network [m].

In the optimal design of fill pipe network,t0andh of slurry with different concentrations can be calculated according to results of L-type pipe gravity flow transportation, and then flow velocity of slurry was calculated according to different flow rate of slurry and pipe diameter. Furthermore, the maximal pipeline length – height ratio that an be reached n the case of different concentrations was calculated and listed in table. So, parameters of fill slurry preparation and pipe network layout were finally determined to make smooth transportation of slurry come true.

5. Case: application in mine engineering

One lead-zinc-silver mine was located in the suburb scenery area. There are town and river just on orebody above. Subsidence of ground surface is not permissible. Ecological environment in mine area and its surrounding area must be strictly protected. No condition can be used for tailings reservoir construction. In addition, grade of ore was very high. So, high-quality cemented filling with unclassified tailings must be performed.

In order to make cemented filling with unclassified tailings structure fluid come true, more systematic lab experiment, pilot test and theoretical analysis and calculation were carried out successively, including determination of unclassified tailings sizes, determination of basic physical-chemical performance and parameters of unclassified tailings, fill slurry ratio optimization test, unclassified tailings settlement property test, determination of unclassified tailings slurry slump, lab and site L-type pipe gravity flow transportation test,

and hydraulic double-cylinder piston pump ( concrete pump) cyclic-pipe test etc, in which results of unclassified tailings slurry slump is shown in Table 1.

According to results from lab L-type pipe gravity flow transportation test, rheology parameters of unclassified tailings slurry with various concentrations were derived, as shown in Table 2. Based on theoretical calculation, the maximal pipeline length – height ratio reached under the condition of different concentrations, flow rates and pipe diameters was shown in Table 3.

Based on results of experimental test above, in combination with concrete conditions in this mine, parameters of fill slurry preparation and transportation were determined as follows:

— Concentration of fill slurry: 70~72%

— Flow rate: 60~80 m³/h

– Inside diameter of fill pipe: 90~100 mm – Flow velocity in pipe: 2.12~3.5 m/s – Transportation drag: 8.10~1.97 kPa/m – Pipeline length – height ratio: 2.07~8.28

On the basis of experimental study above, flow process of filling system was determined, and a new filling system was built. Main flow process of filling system: Concentration of unclassified tailings from ore mill was about 50%, after thickening. These thickened tailings

TABLE 1 Results of unclassified tailings slump test

TABELA 1 Wyniki badania konsystencji odpadów nieklasyfikowanych

Weight concentration

[%]

Slump [cm]

Weight concentration

[%]

Slump [cm]

Weight concentration

[%]

Slump [cm]

80 11 74 23.0 68 28

78 18 72 25.5 66 28

76 21 70 27.0

TABLE 2 Rheology parameters of unclassified tailings slurry with different concentrations

TABELA 2 Parametry reologiczne szlamu odpadów nieklasyfikowanych o ró¿nych stê¿eniach

Slurry concentration, % Rheology parameters 76 74 72 70

t0(Pa) 42.04 25.01 14.61 7.95

?(Pa.S) 24.79 17.41 0.524 0.227

were pressured by sludge pump and piped for 1.4 km, and then to horizontal-type pond for natural settlement at filling station. After waiting for settling to the maximal settling concentration, clear water on the surface of unclassified tailings was discharged, and then pressurized air was used for slurrying so as to make concentration of unclassified tailings in pond homogeneous. At the time of filling, open discharging valve at the bottom of pond so as to transport slurry at a fixed rate into agitator. Cement was fed by a double-tube spiral feeder

TABLE 3 Pipeline length – height ratio for gravity flow transportation with various parameters

TABELA 3 Proporcje d³ugoœci do wysokoœci w transporcie grawitacyjnym o ró¿nych parametrach

Slurry concentrations

[%]

Pipe ID [mm]

Slurry flow rates [m³/h]

40 50 60 70 80 90 100

74

80 × × × × × × ×

90 × × × × × × ×

100 × × × × × × ×

110 × × × × × × ×

125 × × × × × × ×

140 × × × × × × ×

150 1.04 × × × × × ×

72

80 2.468 2.033 1.729 1.504 1.328 1.193 1.081

90 3.73 3.10 2.657 2.321 2.063 1.855 1.686

100 5.295 4.455 3.845 3.383 3.019 2.726 2.485

110 7.172 6.112 5.322 4.714 4.23 3.786 3.462

125 10.476 9.091 8.03 7.19 6.51 5.947 5.473

140 14.22 12.564 11.26 10.195 9.32 8.578 7.95

150 16.91 15.122 13.674 12.479 11.477 10.623 9.88

70

80 5.352 4.436 3.788 3.306 2.932 2.634 2.391

90 6.627 6.695 5.765 5.062 4.512 4.069 3.706

100 11.21 9.526 8.28 7.322 6.563 5.947 5.436

110 14.97 12.89 11.31 10.09 9.094 8.139 7.505

125 21.41 18.81 16.76 15.12 13.76 12.64 11.69

140 28.49 25.50 23.08 21.08 19.39 17.96 16.72

150 33.48 30.30 27.67 25.46 23.61 21.99 20.57

at the bottom of bulk cement silo, metered by spiral electronic scale and added into agitator according to specified proportion. Double horizontal-shaft agitator + high-speed activating agitator were used for stirring in two stages. Unclassified tailings slurry stirred homo- geneously presented as a behavior of structure flow. After flow rate and concentration were checked, slurry flowed into hopper, and then by gravity flow to underground filled area, via filling hole and underground pipeline network.

Behavior of slurry into filling hole was shown in Photo 2. Flowing state that slurry flowed into empty area in stope was shown in Photo 3. Fillbody surface formed after slurry was consolidated and hardened was shown in Photo 4.

Filling system has been put into operation for about 2 years, and presented the following results in mining production.

— Flow process of this system was smooth and stable in operation. Especially, concentra- tion of discharged tailings and slurry was stable. So, specified proportion parameters were stable. This provides a prerequisite for ensuring quality of filing to be stable.

— Fill slurry in pipe and stope presented a structure flow, and segregation and dewa- tering can not occur.

— Slurry consolidated quickly, and its strength can satisfy requirements for upward slicing mining. In the case of cement – tailings ratio = 1 : 4~1 : 6, operation in stope can be performed on the 2^ndday starting after filling.

— “Zero discharge” of tailings and wastes was implemented. All tailings from ore mill were filled into underground mined-out area, wastes from tunneling were filled into stope, and tailings reservoir was unnecessary to be built in mine. In a strict sense,

Phot. 2. Slurry flowed into drillhole Fot. 2. Szlam wp³ywaj¹cy do otworu wierconego

filling with unclassified tailings and “zero discharge” of tailings and wastes were implemented so that ecological environment in mine and its surrounding area was protected effectively.

Phot. 4. Fillbody surface Fot. 4. Powierzchnia wype³nienia Phot. 3. Flowing of slurry in empty area Fot. 3. Przep³yw szlamu w pustej przestrzeni

Conclusions

Based on more systematic lab experiment, theoretical analysis and practical operation, some conclusions can be drawn as follows:

— Unclassified tailings structure fluid slurry was characterized by good flowability, structure flow presenting in pipe and stope empty area, no segregation and dewa- tering, quick consolidation of slurry, and good completeness of fillbody. Its strength satisfied requirements of all mining methods. This is a practical and feasible filling method.

— Flow process of filling system was smooth and stable in operation. In comparison with unclassified tailings thickening – filtering – dewatering in two stages often used in China and other countries, investment in system construction and operating cost were reduced considerably. Meanwhile, technical reliability was higher, and it is easy to put this system into operation.

— In the case of filling with high-quality unclassified tailings, tailings were not nece- ssary to be classified and can be filled underground. In this way, ground surface in mine area can be protected, tailings occupying land was reduced or avoided, and ecological environment in mine and its surrounding area was protected effectively. In addition, this filling provides a good condition for mining production. So, recovery of ore was increased to a maximal extent, and mines obtained the maximal overall economic benefit and good social environment benefit.

As described above, cemented filling with unclassified tailings structure fluid has a very wide prospect for generalized application.

TEORIA I PRAKTYKA USZCZELNIANIA

ZA POMOC¥ CIECZY KONSTRUKCYJNYCH ODPADÓW NIEKLASYFIKOWANYCH

S ³ o w a k l u c z o w e

Wype³nianie odpadami nieklasyfikowanymi, ciecz konstrukcyjna odpadów nieklasyfikowanych, parametry reologiczne, przyk³ady in¿ynierii górnictwa

S t r e s z c z e n i e

Wobec sytuacji wyczerpywania siê zasobów surowcowych i wzrastaj¹cych wymogów ochrony œrodowiska, wykorzystanie odpadów nieklasyfikowanych znajduje coraz szersze zastosowanie w kopalniach metali. Autorzy opisuj¹ obecn¹ sytuacjê wykorzystania odpadów nieklasyfikowanych w Chinach i innych krajach, omawiaj¹ metodê wykorzystania cieczy konstrukcyjnych odpadów nieklasyfikowanych, przeprowadzaj¹ ocenê para- metrów reologicznych cieczy konstrukcyjnych odpadów nieklasyfikowanych oraz analizê teoretyczn¹ i obli- czenia w³aœciwoœci transportowych okreœlonych na podstawie eksperymentów laboratoryjnych, oraz dokonuj¹ wprowadzenia do schematu procesu technologicznego i wyników uzyskanych z zastosowania tej metody w po-

³¹czeniu z praktyk¹ w podsadzaniu.

THEORY AND PRACTICE IN CEMENTED FILLING WITH UNCLASSIFIED TAILINGS STRUCTURE FLUID

K e y w o r d s

Cemented filling with unclassified tailings, unclassified tailings structure fluid, rheology parameters, mining engineering examples

A b s t r a c t

With a further understanding of mineral resources not to be regenerated and an increasingly strictness of requirements for environment protection, unclassified tailings filling has found wider and wider application in metals mines. The author describes present situation of unclassified tailings filling in China and other countries, puts forward filling method for unclassified tailings structure fluid, carries out determination of rheology parameters of unclassified tailings structure fluid and theoretical analysis and calculation of transport property based on lab experiments, and makes an introduction to technological flowchart and operation results of this filling method in combination with practice in mine fill.