STOCK PLEDGE AGREEMENT

         THIS STOCK PLEDGE  AGREEMENT  ("Agreement") is made and entered into as
of the 15th day of December, 2000 by and among Mineral Recovery Systems, Inc., a
Nevada  corporation  ("Pledgor")  and Doral 18,  LLC, a Cayman  Islands  limited
liability company ("Pledgee").

                              Preliminary Statement
                              ---------------------

         A. Altair  International  Inc., an Ontario  corporation  ("Altair") and
Pledgee have agreed to enter into a Securities  Purchase  Agreement  dated as of
December  15,  2000 (the  "Securities  Purchase  Agreement")  pursuant  to which
Pledgee has agreed to purchase from Altair (i) an Asset Backed Exchangeable Term
Note in the form of Exhibit A attached to the Securities Purchase Agreement (the
"Note")  and a Warrant  in the form of  Exhibit  B  attached  to the  Securities
Purchase Agreement (the "Warrant").

         B.  Pledgor  owns one  hundred  percent  (100%) of the shares of common
stock of Altair Technologies, Inc., a Nevada corporation (the "Securities").

         C.  Pledgor  is a  wholly-owned  subsidiary  of Altair  and  expects to
benefit from the proposed  transaction between Altair and Pledgee,  such that it
is and will be in  Pledgor's  interest  and to its  financial  benefit to induce
Pledgee to purchase the Note and the Warrant.

         D. As security  for the  payments to be made to Pledgee by Altair under
the Note, Pledgor desires to pledge the Securities to Pledgee.

         NOW,  THEREFORE,  in consideration of the premises set forth herein, it
is hereby agreed as follows:

1.  Collateral.  The  term  "Collateral"  shall  mean  the  Securities  and  all
dividends,  distributions  and other amounts or  additional  securities to which
Pledgor (with or without  additional  consideration)  is or becomes  entitled by
virtue  of  its  ownership  of any of the  Securities  or as the  result  of any
corporate reorganization,  merger,  consolidation,  stock split, stock dividend,
conversion, preemptive right or otherwise, and the proceeds thereof.
2.                Deposit of  Collateral.  To secure  payment  of the  Pledgor's
obligations  under the Note,  Pledgor hereby pledges and deposits the Securities
with Pledgee and hereby  grants to Pledgee a valid and  perfected  first lien on
and security interest in the Securities and other items of the Collateral.

3.  Representations  and Warranties.  Pledgor hereby  represents and warrants to
Pledgee that as to the Collateral  deposited by such Pledgor with Pledgee on the
date hereof,  (i) Pledgor is the legal and beneficial  owner of such Collateral;
(ii) such Collateral is validly  issued,  fully paid and  non-assessable  and is
registered in the name of Pledgor;  (iii) the pledge of  Collateral  pursuant to
the terms of this Agreement, together with delivery thereof, creates a valid and
perfected  first lien on and security  interest in such  Collateral  in favor of
Pledgee;  (iv) the stock power attached to the certificate(s)  representing such
Collateral have been duly executed and delivered by Pledgor to Pledgee; (v) none
of such  Collateral  is subject  to any lien,  except  for the  perfected  first
security  interest  granted to Pledgee hereby and, so long as any portion of the
Note remains unpaid, Pledgor will not create or permit to exist any lien upon or
with respect to such Collateral without the consent of Pledgee; and (vi) Pledgor
will not sell,  transfer,  convey,  assign or otherwise  divest its interests in
such Collateral, or any part thereof, to any other person.

<PAGE>


4.                Stock    Splits,    Stock    Dividends,     Etc.

                  4.1 Pledgor agrees that if by virtue of Pledgor's ownership of
                  the  Collateral,  Pledgor  becomes  entitled  (with or without
                  additional consideration) to other or additional securities as
                  the   result   of  any   corporate   reorganization,   merger,
                  consolidation,  stock split,  stock  dividend,  conversion  or
                  preemptive right or otherwise, such Pledgor shall: 8.2

                  4.1.1  Cause  the  issuer  of such  additional  securities  to
                  deliver  to  Pledgee  the  certificates  evidencing  Pledgor's
                  ownership  thereof and hereby  authorizes and empowers Pledgee
                  to  demand  the same  from  such  issuer,  and  agrees if such
                  certificates  are  delivered  to Pledgor,  to take  possession
                  thereof in trust for Pledgee;

                  4.1.2  Deliver to Pledgee a stock  power with  respect to such
                  securities, executed in blank by Pledgor;

                  4.1.3  Deliver to Pledgee such other  certificates,  forms and
                  other  instruments  as Pledgee may request in connection  with
                  such pledge.

4.2 Pledgor agrees that such additional securities shall constitute a portion of
the Collateral and be subject to this Pledge Agreement in the same manner and to
the same extent as the securities pledged hereby to Pledgee on the date hereof.

5. Dividend Rights/Voting Power. Unless and until an Event of Default shall have
occurred  under the Note and such  default  shall not have been cured within the
applicable cure period,  Pledgor shall be entitled to receive all dividends paid
on the  Securities  and to exercise all voting powers in all  corporate  matters
pertaining  to the  Collateral  for any purpose  not  inconsistent  with,  or in
violation of, the provisions of the Securities Purchase Agreement or the Note.

6.                Default and Remedies.
                  --------------------
6.1 If an Event of Default shall occur under the Note and such default shall not
have been cured within the applicable cure period, Pledgee, at its option, may:

                  6.1.1 Cause the  Collateral to be registered in its name or in
                  the name of its nominee;

                  6.1.2 Exercise all voting powers  pertaining to the Collateral
                  and otherwise act with respect  thereto as though Pledgee were
                  the owner thereof;

                  6.1.3 Receive all dividends and all other distributions of any
                  kind whatsoever on all or any of such Collateral;

                  6.1.4 Exercise any and all rights of collection, conversion or
                  exchange, and any and all other rights, privileges, options or
                  powers of Pledgor pertaining or relating to the Collateral;

                                        2

<PAGE>

                  6.1.5Sell, assign and deliver the whole, or from time to time,
                  any  part of such  Collateral  at any  private  sale,  with or
                  without demand for performance or advertisement of the time or
                  place of sale or  adjournment  thereof or otherwise,  and free
                  from any right of  redemption  (all of which hereby  expressly
                  are  waived  by  Pledgor)  for cash,  for  credit or for other
                  property, for immediate or future delivery, and for such price
                  and on such  terms  as  Pledgee  in its  sole  discretion  may
                  determine;  and 1.1.1  Exercise any other remedy  specifically
                  granted under this  Agreement or now or hereafter  existing in
                  equity or at law, by virtue of statute or otherwise.

With  respect to the actions  described in each of  subsections  6.1.2 and 6.1.4
above, Pledgor hereby irrevocably constitutes and appoints Pledgee its proxy and
attorney-in-fact  with full  power of  substitution  and  acknowledges  that the
constitution and appointment of such proxy and attorney-in-fact are coupled with
an interest and are irrevocable.

6.2 At any sale made  pursuant  to Section  6.1 above,  Pledgee  may bid for and
purchase, free from any right or equity of redemption on the part of the Pledgor
(the same hereby being  waived and released by Pledgor),  any part or all of the
Collateral that is offered for sale, and Pledgee, upon compliance with the terms
of sale and other applicable federal regulatory  requirements,  may hold, retain
and dispose of such Collateral without further accountability therefor.

6.3 Pledgee shall apply the proceeds of any sale of the whole or any part of the
Collateral and any other monies at the time held by Pledgee under the provisions
of this Agreement in satisfaction of the Note.

6.4 Pledgee  shall not have any duty to exercise any of the rights,  privileges,
options or powers or, except as otherwise  required by law, to sell or otherwise
realize upon any of the  Collateral,  as  hereinbefore  authorized,  and Pledgee
shall not be responsible for any failure to do so or delay in so doing.

6.5 Any sale of all or any  portion of the  Collateral  pursuant  to Section 6.1
above shall  operate to divest all right,  title and  interest of the Pledgor to
the Collateral  which is the subject of any such sale.

6.6 Pledgor  acknowledges  that Pledgee may be unable to effect a public sale of
all or a part of the Collateral or that it may be able to do so only after delay
which might  adversely  affect the value that might be realized upon the sale of
the Collateral. Accordingly, Pledgor agrees that Pledgee may sell the Collateral
or any  part  thereof  in one or more  private  sales to a  restricted  group of
purchasers  who may be required  to agree,  among  other  things,  that they are
acquiring the  Collateral for their own account,  for investment  purposes only,
and not with a view toward the  distribution or resale  thereof.  Pledgor agrees
that any such  private  sale may be at prices or on terms less  favorable to the
owner of the  Collateral  than would be the case if such  Collateral was sold at
public sale, and that any such private sale shall not be deemed not to have been
made in a  commercially  reasonable  manner by virtue of such sale having been a
private sale.

                                        3

<PAGE>


6.7 Pledgee  shall give not less than ten (10)   business   days  prior  written
notice to the Pledgor of any sale  pursuant to this  Section 6.  Pledgor  hereby
agrees that such notice is commercially reasonable.

7. Pledgee's Obligations,  Custodial Agreement,  Performance Rights, Pledge Does
Not Make  Pledgee  Shareholder.  Pledgee  shall  not  have any duty to  protect,
preserve  or  enforce  rights  against  the  Collateral  other  than a  duty  of
reasonable  custodial care of any such  Collateral in its  possession,  it being
understood  that Pledgee shall have no  responsibility  for (i)  ascertaining or
taking action with respect to calls, conversions, exchanges, maturities, tenders
or other matters  relating to the  Collateral,  whether or not Pledgee has or is
deemed to have knowledge of such matters,  or (ii) taking any necessary steps to
preserve  rights  against any parties with respect to the  Collateral,  or (iii)
making any capital  contributions  or other  payments on behalf of Pledgor  with
respect to the Collateral.

8.                Termination  of  Pledge   Agreement.   Upon  the  payment  and
performance in full of all amounts due under the Note, the Pledgee shall deliver
to the Pledgor the Collateral in its  possession  and this  Agreement  thereupon
shall be terminated. 5.
9.               Miscellaneous.

9.1 Each and every right, remedy and power granted to Pledgee hereunder shall be
cumulative  and in addition  to any other  right,  remedy or power  specifically
granted  herein or now or  hereafter  existing in equity or at law, by virtue of
statute  or  otherwise  and may be  exercised  by  Pledgee,  from  time to time,
concurrently or independently and as often and in such order as Pledgee may deem
expedient.  Any failure or delay on the part of Pledgee in  exercising  any such
right, remedy or power, or abandonment or discontinuance of steps to enforce the
same, shall not operate as a waiver thereof or affect Pledgee's right thereafter
to  exercise  the same,  and any single or partial  exercise  of any such right,
remedy or power shall not preclude any other right, remedy or power, and no such
failure,  delay,  abandonment or single or partial  exercise of Pledgee's rights
hereunder  shall be  deemed to  establish  a custom  or  course  of  dealing  or
performance among the parties hereto.

9.3 Any  modification  or  waiver of any  provision  of this  Agreement,  or any
consent to any  departure  by Pledgor  therefrom,  shall not be effective in any
event  unless  the same is in  writing  and  signed  by  Pledgee,  and then such
modification, waiver or consent shall be effective only in the specific instance
and for the specific  purpose  given.  Any notice to or demand on Pledgor in any
event not specifically  required of Pledgee  hereunder shall not entitle Pledgor
to any  other  or  further  notice  or  demand  in the  same,  similar  or other
circumstances unless specifically required hereunder.

                                        4

<PAGE>


9.3 Pledgor agrees that at any time, and from time to time,  after the execution
and delivery of this Agreement,  Pledgor shall,  upon the request of Pledgee and
at the expense of Pledgor,  promptly execute and deliver such further  documents
and do such  further  acts and things as Pledgee  may request in order to effect
fully the purposes of this  Agreement  and to subject to the  security  interest
created  hereby any  property  intended by the  provisions  hereof to be covered
hereby.

9.4 Pledgor agrees that it will warrant,  preserve,  maintain and defend, at its
own expense,  the right,  title and interest of Pledgee in and to the Collateral
and all right,  title and  interest  represented  thereby  against  all  claims,
charges and demands of all persons whomsoever.

9.5 Any notice or other  communication  herein required or permitted to be given
shall  be  in  writing  and  may  be  personally  served,  telexed  or  sent  by
telefacsimile  or United  States mail or courier  service and shall be deemed to
have been given when delivered in person or by courier service,  upon receipt of
telefacsimile  or telex,  or three (3) business days after  depositing it in the
United States mail with postage prepaid and properly addressed. For the purposes
hereof,  the address of each party hereto shall be as provided in the Securities
Purchase  Agreement  hereto,  or  at  such  other  address  as  such  party  may
subsequently advise the other parties hereto.

9.6  In the event that any  provision of this  Agreement is deemed to be invalid
by reason of the operation of any law, or by reason of the interpretation placed
thereon by any court,  this Agreement  shall be construed as not containing such
provision and the invalidity of such provision  shall not affect the validity of
any other  provision  hereof,  and any and all  other  provisions  hereof  which
otherwise are lawful and valid shall remain in full force and effect.

9.7  This Agreement  shall inure to the benefit of the successors and assigns of
Pledgee and shall be binding  upon the heirs,  legatees,  administrators,  legal
representatives, successors and assigns of Pledgor.

9.8  This Agreement may be executed in one or more  counterparts,  each of which
shall be deemed to be an original,  but all of which taken together shall be one
and the same instrument.

9.9 This Agreement  shall be governed by the laws and decisions of the State of
Illinois. 7.18

                                        5

<PAGE>

290790  v2

         IN WITNESS WHEREOF,  the parties have executed this Agreement as of the
date first above written.

                                              PLEDGOR:

                                    MINERAL RECOVERY SYSTEMS, INC.

                                    By: ________________________________
                                    Its: ________________________________



         Accepted by:               PLEDGEE:


                                    DORAL 18, LLC


                                    By: ________________________________
                                    Its: ________________________________


         Acknowledged by:           ALTAIR TECHNOLOGIES,  INC.

                                           By: ________________________________
                                          Its: ________________________________
                                       6