Need help on 'Fire approval' process on Lead merge?

There is an issue in my code while merging lead in Salesforce. The requirement is while merging lead I would like to stop the lead merge if the user is not the owner of the lead and then fire an approval process to owner of lead which is being merged. When the owner approves the lead to be merged, than the lead merge functionality can go on with the process. Below is my trigger on lead (which is working on before delete):-

trigger differentOwnerCheckTrigger on Lead (before delete) {
for(Lead lObj: trigger.Old){
if(lObj.OwnerID != UserInfo.getUserId())
{
lObj.addError('Sorry the lead cannot be deleted as you are not the owner of the lead.Please contact the owner of the lead to continue the process');
Approval.ProcessSubmitRequest submitApproval = new Approval.ProcessSubmitRequest();
submitApproval.setObjectId(lObj.id);
Approval.ProcessResult result = Approval.process(submitApproval);
}
}
}

The trigger stops the lead to be merged and also the approval process is fired but is not assigned to any user.I know that I am missing something over here such that my approval process is firing, but it is not assigning to any user. Can anyone please help me out in this.

Thanks.