Put the celery roots in a large bowl. Stir in the orange juice to prevent browning. Add the persimmons, pomegranate seeds, and mint and toss until well combined. To serve immediately, spoon into salad bowls and sprinkle with the pecans. Stored in a sealed container in the refrigerator, Celery Root Slaw, without the pecans, will keep for 2 days. Sprinkle with the pecans just before serving.