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EXHIBIT 15.7

CONSENT OF AUTHOR

(Pierre Desautels, P.Geo., of AGP Mining Consultants Inc., with
an office at 132 Commerce Park Drive, Suite 246, Barrie, ON, L4N 0Z7)

To:   PolyMet Mining Corp. United States
Securities and Exchange Commission

Re:   PolyMet Mining Corp.s Incorporation by
Reference of the Updated NI 43-101 Technical Report on the NorthMet Deposit,
Minnesota, USA with effective date January 14, 2013 and inclusion of references
to the Technical Report in the Companys Form 20-F for the year ended January
31, 2015.

I, Pierre
Desautels, P.Geo., consent to the incorporation by reference of extracts of the
Technical Report entitled Updated NI 43-101 Technical Report on the NorthMet
Deposit, Minnesota, USA with effective date January 14, 2013 and inclusion of
references to the Technical Report in the Companys Form 20-F for the year ended
January 31, 2015.

I consent to
extracts from, or a summary of, the Technical Report in Item 4D(e), 4D(f) and
4D(g) (the relevant sections) of PolyMet Mining Corp.s 20-F filing with the
Securities and Exchange Commission, for the year ended January 31, 2015.

I confirm that
I have read the relevant sections of the Form 20-F filing for PolyMet Mining
Corp. for the year ended January 31, 2015 and that it fairly and accurately
represents the information in the Technical Report that supports the disclosure.

|Dated this 21stday of April, 2015. | /s/
      Pierre Desautels    
|---------------------------------- | ------------------------------
|                                   | Name: Pierre Desautels, P.Geo.

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EXHIBIT 15.7

CONSENT OF AUTHOR

(Gordon Zurowski, P.Eng., of AGP Mining Consultants Inc., with
an office at 132 Commerce Park Drive, Suite 246, Barrie, ON, L4N 0Z7)

To:   PolyMet Mining Corp. United States
Securities and Exchange Commission

Re:   PolyMet Mining Corp.s Incorporation by
Reference of the Updated NI 43-101 Technical Report on the NorthMet Deposit,
Minnesota, USA with effective date January 14, 2013 and inclusion of references
to the Technical Report in the Companys Form 20-F for the year ended January
31, 2015.

I, Gordon
Zurowski, P.Eng., consent to the incorporation by reference of extracts of the
Technical Report entitled Updated NI 43-101 Technical Report on the NorthMet
Deposit, Minnesota, USA with effective date January 14, 2013 and inclusion of
references to the Technical Report in the Companys Form 20-F for the year ended
January 31, 2015.

I consent to
extracts from, or a summary of, the Technical Report in Item 4D(e), 4D(f) and
4D(g) (the relevant sections) of PolyMet Mining Corp.s 20-F filing with the
Securities and Exchange Commission, for the year ended January 31, 2015.

I confirm that
I have read the relevant sections of the Form 20-F filing for PolyMet Mining
Corp. for the year ended January 31, 2015 and that it fairly and accurately
represents the information in the Technical Report that supports the disclosure.

|Dated this 21stday of April, 2015. | /s/
      Gordon Zurowski    
|---------------------------------- | -----------------------------
|                                   | Name: Gordon Zurowski, P.Eng.

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EXHIBIT 15.7

CONSENT OF AUTHOR

(Karl D. Everett, P.E., of Foth, with an office atEagle
Point II, 8550 Hudson Blvd. North, Suite 105, Lake Elmo, MN 55042)

To:   PolyMet Mining Corp. United States
Securities and Exchange Commission

Re:   PolyMet Mining Corp.s Incorporation by
Reference of the Updated NI 43-101 Technical Report on the NorthMet Deposit,
Minnesota, USA with effective date January 14, 2013 and inclusion of references
to the Technical Report in the Companys Form 20-F for the year ended January
31, 2015.

I, Karl D.
Everett, P.E., consent to the incorporation by reference of extracts of the
Technical Report entitled Updated NI 43-101 Technical Report on the NorthMet
Deposit, Minnesota, USA with effective date January 14, 2013 and inclusion of
references to the Technical Report in the Companys Form 20-F for the year ended
January 31, 2015.

I consent to
extracts from, or a summary of, the Technical Report in Item 4D(g) (the
relevant section) of PolyMet Mining Corp.s 20-F filing with the Securities
and Exchange Commission, for the year ended January 31, 2015.

I confirm that
I have read the relevant sections of the Form 20-F filing for PolyMet Mining
Corp. for the year ended January 31, 2015 and that it fairly and accurately
represents the information in the Technical Report that supports the disclosure.

|Dated this 21stday of April, 2015. | /s/
      Karl D. Everett  
|---------------------------------- | ---------------------------
|                                   | Name: Karl D. Everett, P.E.

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EXHIBIT 15.7

CONSENT OF AUTHOR

(David Dreisinger, Ph.D., P.Eng., of Dreisinger Consulting Inc.,
with an office at 5233 Bentley Crescent, Delta, BC, V4K4K2)

To:   PolyMet Mining Corp. United States
Securities and Exchange Commission

Re:   PolyMet Mining Corp.s Incorporation by
Reference of the Updated NI 43-101 Technical Report on the NorthMet Deposit,
Minnesota, USA with effective date January 14, 2013 and inclusion of references
to the Technical Report in the Companys Form 20-F for the year ended January
31, 2015.

I, David
Dreisinger, Ph.D., P.Eng., consent to the incorporation by reference of extracts
of the Technical Report entitled Updated NI 43-101 Technical Report on the
NorthMet Deposit, Minnesota, USA with effective date January 14, 2013 and
inclusion of references to the Technical Report in the Companys Form 20-F for
the year ended January 31, 2015.

I consent to
extracts from, or a summary of, the Technical Report in Item 4D(e), 4D(f) and
4D(g) (the relevant sections) of PolyMet Mining Corp.s 20-F filing with the
Securities and Exchange Commission, for the year ended January 31, 2015.

I confirm that
I have read the relevant sections of the Form 20-F filing for PolyMet Mining
Corp. for the year ended January 31, 2015 and that it fairly and accurately
represents the information in the Technical Report that supports the disclosure.

|Dated this 21stday of April, 2015. | /s/
      David Dreisinger           
|---------------------------------- | -------------------------------------
|                                   | Name: David Dreisinger, Ph.D., P. Eng

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EXHIBIT 15.7

CONSENT OF AUTHOR

(William Murray, P.Eng, of Optimum Project Services Ltd., with
an office at 6440 Gibbons Drive, Richmond, B.C., V7C 2E1)

To:   PolyMet Mining Corp. United States
Securities and Exchange Commission

Re:   PolyMet Mining Corp.s Incorporation by
Reference of the Updated NI 43-101 Technical Report on the NorthMet Deposit,
Minnesota, USA with effective date January 14, 2013 and inclusion of references
to the Technical Report in the Companys Form 20-F for the year ended January
31, 2015.

I, William
Murray, P.Eng., consent to the incorporation by reference of extracts of the
Technical Report entitled Updated NI 43-101 Technical Report on the NorthMet
Deposit, Minnesota, USA with effective date January 14, 2013 and inclusion of
references to the Technical Report in the Companys Form 20-F for the year ended
January 31, 2015.

I consent to
extracts from, or a summary of, the Technical Report in Item 4D(e), 4D(f) and
4D(g) (the relevant sections) of PolyMet Mining Corp.s 20-F filing with the
Securities and Exchange Commission, for the year ended January 31, 2015.

I confirm that
I have read the relevant sections of the Form 20-F filing for PolyMet Mining
Corp. for the year ended January 31, 2015 and that it fairly and accurately
represents the information in the Technical Report that supports the disclosure.

|Dated this 21stday of April, 2015. | /s/
      William Murray   
|---------------------------------- | ---------------------------
|                                   | Name: William Murray, P.Eng

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