# Molybdenum Depletion Including Recycling

L. David Roper

http://www.roperld.com/personal/RoperLDavid.htm

2 July, 2016

Molybdenum is used to make high-strength steel alloys. The graph below shows the molybdenum extraction data for the world and two Verhulst functions fits to the data in order to extrapolate into the future.

Molybdenum extraction rate for the world and a several Verhulst functions fit to the data.

The red curve is a fit with total amount to be extracted which incorporates the latest reserves estimate (~11 x 10^{6} tonnes.

It appears that world-molybdenum extraction will peak by 2025.

Taking an average extraction curve of the two fits, the crossover point at year ~2025 when the amount extracted is equal to the amount left to be extracted is shown here:

## Recycling

Assume that:

- The molybdenum-extraction curve is the average of the two curves given above.
- Recycling of molybdenum follows a hyperbolic tangent curve from 10% to 60% recycling with a break point of year 1980 and width 50 years.
- The recycling is delayed by a Gaussian curve peaking at a delay of 20 years and a width of 10 years.

The effective molybdenum available for making items after the first ten recycling cycles is shown in the following graph, along with the effective molybdenum available for each cycle:

The equation for a recyling cycle is

,

where E_{i} is the amount available from the previous cycle. Here is an example of the Excel coding:

{=(($J$2+$I$2)/2+(($J$2-$I$2)/2)*TANH((A27-$K$2)/$L$2))*SUM($I$27:I27*(EXP(-1*((A27-$A$27:A27-$N$2)/$O$2)^2/2))/$O$2/SQRT(2*PI()))} (The curly bracket surrounding the term makes it into an array; it must be entered by holding down the SHIFT & CTRL keys while pressing the ENTER key.)

Of course, the recycling could be extended to more cycles, skewing the curve further into the future. However, the peak and fall off after it will not change because further cycles are essentally zero in that time region.

Thus, under the assumptions given above, the effective amount of molybdenum available for making items peaks at about 2035 and falls off rapidly after that. Humans will have taken concentrated molybdenum deposits and scattered them across the surface of the earth.

The Excel spreadsheet is set up to make it easy to calculate with different recycling assumptions.

Minerals Depletion