MeltObject.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class MeltObject : MonoBehaviour
{
    public GameObject particlePrefab;
    public string targetTag = "Lava";
    public float objectDestroyDelay = 1f;

    private void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.CompareTag(targetTag))
        {
            Instantiate(particlePrefab, transform.position, transform.rotation);
            Destroy(gameObject, objectDestroyDelay);
        }
    }
}

Super simple Unity script for instantiating a flame particle prefab and then destroy the object the script is attached to.