For large-scale new heap leaching projects, feasibility studies are required to carry out technical scheme selection and economic effect evaluation. The existing production mines use a heap leaching process to reduce production costs. Projects that improve economic efficiency can be evaluated according to the requirements of national expansion and reconstruction projects. Although it is basically the same as the feasibility study in the indicators and selection criteria of economic evaluation, the calculation range of benefits and costs is different from the principle of comparability.

In terms of comparability, expansion and reconstruction projects should adopt the “with or without contrast method”. That is to calculate the incremental benefits and incremental costs corresponding to the expansion and reconstruction, and after expansion and reconstruction, and continue to operate. For the reconstruction project that does not increase the output and only reduces the production cost (such as the current uranium mine for heap leaching), the cost savings are incremental benefits, and the return on new investment is the cost savings and the number of new investment. ratio. This will greatly simplify the workload of technical and economic evaluation.

To carry out expansion, renovation project of the existing heap leach mine production, due to the nature of the ore grade, still leaching of total metal reserves, local natural geographical environment and economic conditions, raw material prices, the cost of business management and many other factors are Clear, so as long as there is an ore heap leaching test report, its leaching characteristics and parameters (such as C p , C mn and Cav ), leaching period, leaching amount, etc., can be generally evaluated.

The total investment for the reform and expansion project is CAP, the total income is REV, the total expenditure is PC, the benefit coefficient is PF, the static investment return time is d (by day), the total profit is P, and the maintenance fee is R. , the unit price of metal sales price is MP, then

PF=REV∕PC (1)

Or PC=REV∕PF (2)

The total daily income is

REV∕d=MP(C av ·Q)(1-R) ​​(3)

Where Q is the volume of the daily leachate.

The total daily expenditure is

PC/d = daily operating expenses E + the number of investments that should be repaid each day G (4)

The number of investments that should be repaid each day is

G=CAP∕d=CAP(C av ·Q)∕W (5)

Where W is the amount of metal that the mine can still leach (recycle). Substituting equations (3), (4), and (5) into equation (2),

E+CAP(C av ·Q)∕W=(C av ·Q)(1-R)MP∕PF (6)

To solve equation (6), you can get the following two formulas:

PF=W(C av ·Q)(1-R)MP∕[W·E+CAP(C av ·Q)] (7)

C av =[(E+CAP∕d]∕[(1-R)Q·MP∕PF] (8)

If the formula (7) or (8) is used for the economic evaluation of the expansion and reconstruction of some old mines, it is concise and quick. For example, in recent years, due to the decline in the price of the international uranium market and the increase in the prices of domestic raw materials, some uranium mines have reduced the production cost and changed the conventional agitation leaching to heap leaching projects. If formula (7) is used for technical and economic evaluation. , it is faster and simpler than the feasibility study. Because of the eight parameters of equation (7), W, MP, and R are known, Cav and Q are provided by the column immersion test, and the remaining three parameters are compared when comparing CAP and E of different production scales. It can be obtained intuitively and clearly.

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