Dissolve orange gelatin in boiling water in a bowl; stir in cold water, salt, and reserved pineapple juice. Chill until partially thickened, about 45 minutes. Mix carrots, celery, pecans, and pineapple into gelatin and pour into prepared gelatin mold. Refrigerate until firm, at least 2 more hours. Invert mold onto serving platter to release gelatin salad.